A reformist candidate critical of many of the Iranian government’s policies, including the mandatory head scarf law, will compete next week against a hard-line conservative in a runoff election for the country’s presidency, Iran’s interior ministry announced on Saturday. The runoff follows a special vote called after the death last month of the previous leader, Ebrahim Raisi, in a helicopter crash.

A second round of voting, which will pit the reformist, Masoud Pezeshkian, against Saeed Jalili, an ultraconservative former nuclear negotiator, will take place on July 5. The runoff was in part the result of low voter turnout and a field of three main candidates, two of whom competed for the conservative vote. Iranian law requires a winner to receive more than 50 percent of all votes cast.

The majority of Iranians, 60 percent, according to Iran’s state news agency, did not vote on Friday, in what analysts and aides to the candidates said was largely an act of protest against the government for ignoring their demands for meaningful change.

A prominent Iranian economist, Siamak Ghassemi, said on social media that the voters were sending a clear message. “In one of the most competitive presidential elections, where reformists and conservatives came to the field with all their might, a 60 percent majority of Iranians are through with reformist and conservatives.”

Iran is facing multiple challenges, from domestic turmoil to international tensions. Its economy is cratering under punishing Western sanctions, its citizens’ freedoms are increasingly curtailed and its foreign policy is largely shaped by hard-line leaders.

The campaign, which initially included six candidates — five conservatives and one reformist — was notable for how candidly those issues were discussed and a public willingness to attack the status quo. In speeches, televised debates and round-table discussions, the candidates criticized government policies and ridiculed rosy official assessments of Iran’s economic prospects as harmful delusions.

Public dissatisfaction in any new president’s ability to bring change was reflected in the paltry turnout, a historic low for presidential elections and even less than the reported level of 41 percent in parliamentary elections earlier this year. The low totals will be a blow to the country’s governing clerics, who made voter participation a marker of the vote’s perceived legitimacy and had hoped to achieve a 50 percent turnout.

In the official results announced on Saturday, Dr. Pezeshkian led with 10.4 million votes (42.4 percent), followed by Mr. Jalili at 9.4 million (38.6 percent). A third conservative candidate, Mohammad Baqer Ghalibaf, the current speaker of Parliament and former mayor of Tehran, was a distant third at 3.3 million (13.8 percent).

It remains unclear whether a runoff between two candidates representing different ends of the political spectrum will inspire more voters to come out, when large numbers of Iranians see the candidates as part of a system they want to reject wholesale.

“This is going to be a very difficult and challenging week,” Mohammad Mobin, an analyst in Tehran who worked on the campaign of Dr. Pezeshkian, said on Saturday. “To get voters out we have to be strategic.” He added, speaking about the conservatives, “People think there is no difference between us and them.”

Simple math would seem to indicate that Mr. Jalili would surpass 50 percent if he picked up Mr. Ghailibaf’s votes. But in earlier polling, many of those voting for Mr. Ghalibaf said they would not support Mr. Jalili. And Dr. Pezeshkian might pick up votes from those dreading the prospect of a Jalili presidency.

In a neighborhood in north Tehran on Saturday, a group of men discussed the election results, and the prospects for the runoff, over coffee. One of them, Farzad Jafari, 36, predicted a higher turnout in the next vote. He and others also debated whether Mr. Jalili would be able to unite the conservative vote in a head-to-head contest, or if even more voters would emerge to back the reformist option offered by Dr. Pezeshkian.

Mr. Jafari said he thought many of those who, like him, sat out Friday’s voting might well be drawn back for the runoff. “I did not want to vote at all because they excluded those who should’ve been in the race, they were mostly reformers” he said. “But more people will vote next time in the next round and those who cast a blank vote, or who didn’t vote will come.”

Besides domestic pressures, Iran’s leaders are also facing an especially volatile time in the region: Israel’s war in Gaza against Hamas, an Iranian-backed militant group, and an escalation in skirmishes between Israel and Hezbollah pit two of Iran’s proxy forces against Israel, its sworn enemy.

Despite the critical rhetoric of the campaign, the candidates were all members of the Iranian political establishment, approved to run by a committee of Islamic clerics and jurists. All but one, Dr. Pezeshkian, were considered conservatives close to the country’s supreme leader, Ayatollah Ali Khamenei.

Mr. Jalili, a former nuclear negotiator, is likely the candidate closest to Mr. Khamenei. He leads the ultra-right-wing Paydari party and represents the country’s most hard-line ideological views when it comes to domestic and foreign policy. Mr. Jalili has said he does not believe Iran needs to negotiate with the United States for economic success.

Dr. Pezeshkian is a cardiac surgeon and veteran of the Iran-Iraq war who served in Parliament and as Iran’s health minister. After his wife died in a car accident, he raised his other children as a single father and never remarried. This and his identity as an Azeri, one of Iran’s ethnic minorities, has endeared him to many voters.

Dr. Pezeshkian was endorsed by a former reformist president, Mohammad Khatami, and he has expressed openness to nuclear negotiations with the West, framing the debate as an economic issue with the ultimate aim of escaping economic sanctions over its nuclear and ballistic missile programs.

After a bitter public spat, Mr. Ghalibaf issued a statement on Saturday endorsing Mr. Jalili and asked his voters to do the same to ensure victory for the conservative camp.

By stacking the deck to increase the chances of a conservative’s victory, Mr. Khamenei signaled his desire for a second in command whose outlook mirrored his own and who would continue the agenda of Ebrahim Raisi, the hard-line president killed last month in a helicopter crash near the border with Azerbaijan.

The low voter turnout reflected widespread apathy among Iranians, whose frustration has been intensified by the government’s violent crackdowns on protesters demanding change and its inadequate response to the toll that decades of sanctions have wreaked on the country’s economy, shrinking Iranians’ purchasing power.

The most recent anti-government demonstrations — and an ensuing crackdown — were prompted largely by the 2022 death of Mahsa Amini, who died in police custody after being detained for incorrectly wearing her mandatory head scarf, or hijab.

In a nod to the unpopularity of the hijab law, the candidates all sought to distance themselves from the methods the country’s morality policy use to enforce it, which include violence, arrests and fines.

Although a new president could soften the enforcement of the head scarf mandate, as Mr. Khatami and a moderate president, Hassan Rouhani, did in their terms in office. it is unlikely that the law would be annulled.

That is largely because Iran is a theocracy with parallel systems of governance, in which elected bodies are supervised by appointed councils made up of Islamic clerics and jurists. And major state policies on nuclear, military and foreign affairs are decided by the country’s supreme leader, Mr. Khamenei.

The president’s role is focused on domestic policy and economic matters, but it is still an influential position. Mr. Rouhani, for example, played an active role in forging the 2015 deal with the Western powers in which Iran agreed to scale back its nuclear program in exchange for the easing of sanctions.

The Trump administration withdrew the United States from that deal in 2018, and Iran has since returned to enriching uranium. Beyond tensions over Tehran’s nuclear program, the United States and Iran have in the past year come increasingly close to a direct confrontation as they compete for influence across the Middle East.

In Gaza, the war between Israel, a U.S. ally, and Hamas has drawn the United States, Iran and Iran’s foreign proxies into closer conflict. Iran sees its use of these groups as a way of extending its power, but many citizens, particularly in the cities, see little value in their leaders’ strategy and believe the economy will recover only through sustained diplomacy and the lifting of sanctions.“We are in a Third World country and we are sitting on top of so much wealth ,” said Vahid Arafati, 38, a coffee shop owner in Tehran, after he voted on Friday. “For instance the Arab states are getting benefits from their wealth, but with our politics we cannot get anything.”

Asked why he voted if he did not expect much change, he said, “Maybe I have a little hope.” After a pause, he added: “Isn’t it good to have a little hope?”

Leily Nikounazar contributed reporting.