Two moderate political parties announced today that they would boycott the Iranian election for a constitutional assembly Friday ensuring a clear victory for Moslem clergymen and other hard-line supporters of Ayatollah Ruhollah Khomeini.

The two parites, the Moslem People's Republican Party and the National Front, both complained about the conditions under which the election was being held.

About 1,000 candidates are vying for the assembly's 73 seats. The delegates will debate and amend the draft constitution of the Islamic republic.

No official lists of candidates are available to the public but a high proportion -- according to some estimates as many as 80 percent -- are clergymen.

The Moslem People's Republican Party draws much of its support from moderate regligious leader Ayatollah Kazem Shariatmadari. The party announced its decision to boycott the elections after the government rejected its request for a three-week postponement on the ground that there had been too little time to organize the election campaign.

The National Front, which took a leading role in opposing the shah, accused the government of failing to dispel "the prevailing atmosphere of repression" and objected that "nondemocratic criteria were imposed on the candidates and the elections are monopolize by the clergy."

A week ago, another moderate political group, the National Democratic Front, announced it would boycott the elections because of the new government's and its choice of a small assembly to debate the constitution instead of a large constituent assembly.

Refusal of the moderates to participate in the elections leaves only the Islamic Republican Party, made up of Hard-line backers of Khomeini, and several small, left-wing organizations.

There are also several individual candidates-notably the popular religious moderate Ayatollah Mahmoud Taleghani -- standing on the strength of their personal reputations.

It is unlikely that the boycotts will have a great effect on the vote's outcome. Of the parties, the Islamic Republicans were favored, having put up the most candidates and being backed by a strong organization that could point to apparent ties to Khomenini.

Yet the boycotts clearly indicate the nature of the opposition to Khomeini, who only two days ago advised the people of Iran that it was their religious duty to vote, calling at the same time for the election of "believers in Islam" and those who "shun affiliation to left or right."

Furthermore, the boycotts breach the facade of unity upon which Kholmeini has capitalized since the March referendum on whether to have an Islamic republic or a monarchy. In that vote the authorities claimed the support of no less than 98 percent of a surprising 22 million voters.

In Tehran, millions of voters appeared to have litle Chance of learning about the election boycott. The capital's two main newspapers carried front-page stories saying the Moslem People's Republican Party would definitely take part. CAPTION: Picture, Potential voters read party declarations in Tehran on the eve of election to Irania constitutional assembly. UPI