Iranian police quelled Moslem religious dissidents in the provincial city of Qum yesterday by opening fire on a crowd, the government disclosed today.

It said six people were killed, including a youth who was trampled to death, when police fired on right-wing demonstrators who are opposed to the shah's land reforms and emancipation of women. Dissident sources said the casualties were much higher.

The incident -- the first reported instance in recent years of government forces having fired on a crowd -- coincided with appeals for support to visiting U.N. Secretary General Kurt Waldheim by a new group of Iranian human rights activists here.

The shooting at Qum, about 90 miles south of here, marked the worst violence to date in the Shah's current crackdown against opponents on both ends of the political spectrum.

Last week President Carter said after a visit to Iran that the shah "is deeply concerned about human rights" and that in some aspects of human rights Iran has experienced considerable progress over the last 20 years.

Dissident sources here said about 20 persons were killed in the Qum incident and more than 100 others were injured. They claimed that the demonstration was peaceful until the crowd was attacked by police. Government spokesmen said police resorted to violence after the demonstrators attacked one of their precinct station.

The demonstration stemmed from an incident Saturday in which police broke up a sitin staged by tehological students to protest government propaganda against a radical religious leader, Ayatollah Khomeini, who now lives in exile in Iraq.

Dissidents said shops and the bazaar in Qum, a city known for its religious fervor, have shut down to protest the shooting. The authorities have closed schools and mosques and arrested about 70 persons, they said.

The arrival of Waldheim for talks on the Middle East situation today generated considerable activity among Iranian intellectuals who oppose the shah's authoritarian rule.

Iranian opposition leaders have scheduled a rare press conference to voice their demands for political liberalization. In related developments, 95 members of the dissident Writers Association of Iran as well as the newly formed Iranian Committee for the Defense of Liberty and Human Rights have both sought meetings with the U.N. secretary general.

The latter group also issued a letter signed by 23 prominent Iranians and citing 15 areas of human rights violations by the Iranian government.

Addressed to Waldheim, it calls on the United Nations to help the Iranian people establish freedom, democracy and the enforcement of the principles of the Iranian constitution. The letter also accuses Shah Mohammad Reza Pahlavi of pushing the country toward political instability and economic decline through his authoritarian rule.

Among alleged human rights violations, the group lists "the practice of all modes of physical and mental torture," continued detention of political prisoners without trial and refusal to free a number of others whose sentences have expired.

Carter, who visited Tehran on New Year's Eve, briefly and subtly raised the issue of human rights in a banquet toast to the shah.