A landmark antitrust trial against Google concluded on Friday after a federal judge heard final arguments, setting the stage for a ruling that could fundamentally shift the tech industry’s power.

“The importance and significance of this case is not lost on me, not only for Google but for the public,” Judge Amit P. Mehta said in the final moments of the proceedings on Friday. He thanked the lawyers who argued the case, and then added, “I guess you’ve passed the baton to us.”

Now, he must decide the case in which the Justice Department and state attorneys general say that Google has abused a monopoly over the search business, stifling competitors and limiting innovation, something the company denies.

During two days of closing arguments, Judge Mehta of the U.S. District Court for the District of Columbia did not reveal how he planned to rule. He grilled both sides, frequently referencing testimony and evidence from the 10-week trial last year to poke holes in their arguments. He also demanded that they explain how their positions fit with major legal precedents.

As the proceedings closed on Friday, Kenneth Dintzer, the Justice Department’s lead trial lawyer, argued that if antitrust laws “cannot thaw” a search business dominated by Google, the company’s practices will continue into the future.

John E. Schmidtlein, Google’s lead lawyer, countered that a ruling in favor of the government “would be an unprecedented decision to punish a company for winning on the merits.”

Judge Mehta’s ruling in the coming weeks or months will probably influence the course of other government antitrust lawsuits against Apple, Amazon and Meta, the owner of Instagram and WhatsApp, as U.S. regulators try to rein in their power.

The government argues Google illegally cemented a monopoly in search by paying Apple and other tech partners billions of dollars to feature the Google search engine in their products.

On Friday, the discussion focused on the government’s second claim that the company also has a monopoly over the ads that run in search results.

Google pointed to other companies that compete in search and advertising.

“Facebook, Instagram, TikTok, Amazon — all of these companies have very, very detailed and very useful information that allows them to give advertisers lots and lots of different options to reach the consumer groups they’re most interested in,” Mr. Schmidtlein argued.

Judge Mehta asked the Justice Department, to explain why search ads were so different from ads on Facebook and other social platforms.

“How does that measure up with reality?” he asked. “It can’t be that Facebook’s ad platform is an inferior product and they’re making billions of dollars.”

Judge Mehta also mentioned the success of TikTok, which, he said, had a “pretty good ad platform” and was growing. He said he had spent some time using TikTok’s search to research the case.

In a seeming nod to national security concerns about that app, he added: “Not that I have it on my phone, just to be clear.”

The government also said the judge should sanction Google for a company policy that automatically turned off the history for workplace chats, arguing that the policy resulted in the destruction of evidence. Mr. Dintzer said the court needed to “say this is wrong” to stop Google from hiding evidence in the future. A lawyer for Google, Colette T. Connor, denied the company had done anything inappropriate.

“Let me just be perfectly candid,” Judge Mehta said. “Google’s document retention policy leaves a lot to be desired.”

On Tuesday, Google’s employees gathered for an all-hands meeting named T.G.I.F. These companywide meetings are rarely held on Fridays these days, but the name has stuck.

Executives shared highlights from a recent earnings report and cloud-computing conference, and warned workers against taking disruptive actions in the wake of internal protests against a cloud-computing contract with Israel.

But no one in the meeting, two employees said, broached a topic that could have a dramatic impact on Google: its landmark antitrust trial with the Justice Department, where arguments are finally coming to an end this week.

For eight months, while tech policy experts have tried to divine what a Google victory or loss would mean for the power of tech giants in the United States, Google’s employees have mostly ignored the antitrust fight, according to interviews with a dozen current and recent workers, who asked not to be identified because they were not authorized to discuss the legal matter.

Even among Google’s outspoken employees, the legal risks facing the company have become background noise. For two decades the company has been one of Silicon Valley’s apex predators, and its workers have grown accustomed to Google’s breezing past regulatory scrutiny. Why expect something different this time?

Besides, they added, the more pressing threat to Google is a competitive one posed by Microsoft and OpenAI, the maker of the ChatGPT chatbot. (The New York Times sued OpenAI and Microsoft in December for copyright infringement of news content related to A.I. systems.)

Closing arguments in the trial began on Thursday in U.S. District Court for the District of Columbia and are expected to last two days. The Justice Department has taken aim at Google’s search business, claiming the company illegally extended its monopoly by forging default search deals with browser makers, such as Apple and Mozilla. Google has said that the contracts are legal and that its innovations have broadened competition, not constricted it.

Peter Schottenfels, a Google spokesman, said in a statement that the Justice Department’s case “is deeply flawed.”

“Our employees know that we face intense competition — we experience it every day,” Mr. Schottenfels said. “That’s why we are focused on building innovative and helpful products that people choose to use.”

On Thursday, Judge Amit P. Mehta stress-tested the Justice Department’s and Google’s arguments in court. He prodded the Justice Department on its assertion that Google’s market power had hindered its search engine’s innovation or quality for consumers.

“I’m struggling to see how I could reach findings of fact that would say, ‘Google has not done enough,’ or ‘Google’s product has worsened over the course of 10 years,’ in such a way that I could say it’s because of lack of competition,” Judge Mehta said.

He also questioned Google’s assertion that it faced competition from sites like Amazon, where consumers go to search for pricing and other results while shopping, saying the average person would see a difference between Google and Amazon.

Soon, it will be up to Judge Mehta to decide. If Google loses, there is a wide range of potential consequences. Google could be forced to make small changes to its business practices or face a ban on the types of default contracts that have helped make its search engine ubiquitous. The Justice Department could also call for the divestiture of one of Google’s search distribution platforms like the Chrome browser or the Android mobile operating system — a drastic but less likely outcome.

For more than a decade, Google has faced fines and government lawsuits in Europe and elsewhere, while notching significant revenue and profit gains. That has made all the legal wrangling look like the cost of doing business to some employees, two people said.

Google employees have been taught to avoid talking or writing about lawsuits. The company always tells employees to “communicate with care,” as laid out in an internal document reviewed by The Times. In other words, what you write can end up becoming an embarrassing bit of evidence in court.

When an employee in Google’s advertising department recently mentioned news articles about the antitrust lawsuit at the office, co-workers shook their heads and said, “We don’t talk about that,” the person said.

But lawsuits happen all the time. In the last six months, Google has settled cases at a steady clip, ending privacy, patent and antitrust claims against the company. Those suits didn’t cause much to change, leading some employees to believe that this case is no different.

When employees do talk about the Justice Department suit, they echo one of the company’s arguments: that the allegations against Google Search are outdated, especially as the tech industry has rushed to develop artificial intelligence systems that could alter the search market, two people said.

Some employees expect all the legal hype around the search case to boil down to small business tweaks and some fines, two people said.

Despite the confidence of employees, William Kovacic, a former chairman of the Federal Trade Commission, said in an interview that companies targeted for antitrust violations often lost a step, citing IBM and Microsoft. He expects Google to have a similar experience, he said.

The lawsuits can “inject a little more caution into how the company operates,” said Mr. Kovacic, who now teaches competition at George Washington University. “To some degree, I feel they’ve already lost. They’ll never be the same.”

Google’s executives had hoped employees would ignore the Justice Department suit. When it was filed in the fall of 2020, Sundar Pichai, the company’s chief executive, told employees to stay focused on their jobs and not let it distract them.

Kent Walker, the company’s chief legal officer, said he had assigned several hundred employees to work on Google’s defense, with the litigation led by three outside law firms and dozens of in-house lawyers.

In the years since, Mr. Pichai hasn’t usually mentioned the suit and downplayed it when addressing employees at all-hands meetings, three people said. And the company has reiterated the need to be mum, sending emails to employees instructing them not to discuss the case publicly or with the press, two people said.

Lately, other issues have captured workers’ attention more. On Memegen, a forum that serves as Google’s virtual water cooler, a person said, commenters have continued to discuss topics like the ongoing layoffs, jobs moving to India and protests against the Israeli cloud deal, known as Project Nimbus, which led Google to fire 50 participants for disrupting and occupying workspaces.

On Tuesday, Mr. Pichai said that it was fine for employees to disagree about sensitive topics, but that they could not cross the line.

“We’re a business,” he said.

David McCabe and Cecilia Kang contributed reporting from Washington.