Islamic militiamen fired in the air today to disperse thousands of Iranian women defiantly marching on Prime Minister Mehdi Bazargan's office to protest the increasingly antifeminist overtones of Iran's fundamentalist Moslem revolution.

No one was hurt. But the spectacle of perhaps 15,000 women diving for cover behind parked cars and buildings inevitably marked yet another stage in the declining popularity of Ayatollah Ruhollah Khomeini, the unofficial ruler.

Some women even shouted "Down with Khomeini" inwhat was believed the first such show of open hostility since he returned Feb. 1 from more than 14 years of exile.

Three, and perhaps as many as five, separate meetings called to mark International Women's Day converged in the march on the prime minister's office through heavy snow and slush. The march reflected growing polarization between the Moslem fundamentalists and Iran's lay minority.

The chanted slogans showed women's exasperation with Khomeini's fundamentalist Islam rule.

In recent days, at his instigation, the government has ordered the suspension of a law against bigamy and arbitrary divorce, banned abortion, ended coeducation and ordered women civil servants to wear in govrnment ministries a head scarf or full-length cloak known as the chador.

The bare-headed demonstrators were heckled by men and a counter-demonstration of chador-clad women and male supporters.

At one point the counterdemonstrators tipped snow-laden tree branches onto the marching women.

In yet another Islamic-dictated decision. Defense Minister Hamid Madani announced today that henecforth women no longer are liable for compulsory military service.

Dressed in blue jeans, jackets -- acceptable Western attire befoe Khomeini's return -- and without a single chador, the women and their husbands and boyfriends marched out from Tehran University and crossed a main artery before heading toward Bazargan's office. Many were high school and university students, but there was a sprinkling of older women.

"Death to dictatorship," "We won't wear the chador." "Bazargan -- do not abandon us," were among the slogans chanted by the demonstrators.

Many marchers brandished the traditional left-wing symbol of the clenched fist. Elsewhere the Organization of Iranian Women, the shah-era women's organization that theoretically had been disbanded, held a large meeting.

American fominist Kate Millet, here to help Iranian women's organizations, said at a meeting this afternoon that Iran "right now is the heart of our struggle." She brought greetings from Simone de Beauvoir, Angela Davis, Gloria Stemem and other prominent women.

About 3,000 other women were reported to have left by bus for Qom, the holy Shiite Moslem city 90 miles due south of Tehran, to bring their protest to Khomeini who took up residence there a week ago.

A delegation of 300 other women -- accompanied by their children -- was also seeking an audience with the ayatollah to protest their fate as dependents of foreigners now being expelled from Iran in the current wave of xenophobia.

Clearly concered about the politically explosive issue of women's rights, Khomeini tonight issued a statement saying that those caught insulting women in the name of his revolutionary authority should be severely punished, Reuter reported.

[In a separate statement, the ayatolah defended the chador as the "flag of the revolution."]

Further signs of Khomeini's declining fortunes were the number of his pictures apparently torn down in Tehran.

Compared to only a few days ago, there dhas been a proliferation of pictures of Mohammed Mossadegh, the late nationalist prime minister ousted by the shah in a CIA-backed coup in 1953, and of Ayatollah Mahmoud Taleghani, the more open-minded cleric Khomeini left behind as his principal lieutenant when he moved to Qom.