President Abol Hassan Bani-Sadr today pledged to investigate the "many complaints of cheating" in postrevolutionary Iran's first parliamentary election and cancel the vote if fraud and vote-rigging prove "widespread and serious."

The warning, reported by the official Pars News Agency, was widely interpreted as a criticism of the right-wing clerical islamic Republican Party, which opposes Bani-Sadr and holds a commanding first-round lead based on incomplete results.

Some analysts suggested that Bani-Sadr in effect was appealing indirectly to all the Islamic Republican Party's rivals to unite to fight the clerical hardliners in the crucial runoff vote scheduled for early April.

At stake is the fate of the estimated 50 U.S. hostages held since Nov. 4. Iran's revolutionary leader, Ayatollah Ruhollah Khomeini, has said their fate is to be decided by the new parliament, which is not expected to take up serious business until May. New elections because of fraud in some districts apparently would set back parliamentary consideration of the hostages' release still further.

Bani-Sadr has called for a quick resolution of this issue. The Islamic Republican Party has firmly backed the radical Islamic students holding the hostages.

With both the counting and voting the objects of charges and countercharges of malpractice by rival political parties, 37 of the 51 candidates elected by the necessary absolute majority to the 270-seat parliament were from the Islamic Republican Party.

More than two days after the polls closed, runoffs were ordered in 71 other voting districts where candidates failed to meet the absolute majority requirement. As many as half the total seats may have to be decided in such runoffs.

Causing further uneasiness was an announcement from the vice president of election headquarters that definitive results from the single, citywide 30-seat Tehran voting district "most probably" would be delayed until after the week-long Iranian new year holiday starting Thursday.

Officials at the Interior Ministry, controlled in large part by the Islamic Republican Party, had announced that final first-round results might not be announced before Thursday.

In the exchange of fraud charges, the Marxist-Leninist Fedayan guerrillas were accused of voting the dead in Tehran by using birth certificates of deceased Iranians to obtain the complicated ballot sheet.

In Fars Province in Central Iran, 46 ballot boxes were burned by unidentified party stalwarts apparently unhappy with what they feared would be results favoring their rivals.

The leftist Islamic Mujaheddin party wrote Bani-Sadr demanding a new vote in Tehran "in view of the frequent cheating." The party specifically asked that computers be used for tallying any new election.

The Islamic Republican Party, in turn, charged the Fedayan and Mujaheddin with violating the election regulations by continuing to campaign after the legal cut-off date, an accusation that these leftist parties also made against the Islamic Republicans.

Another charge was that party workers often filed out the complicated ballots for illiterate voters estimated to make up 70 percent of the electorate.

In turbulent Kurdistan, where three candidates backed by the still formally banned Kurdistan Democratic Party won handily, Interior Ministry officials are now threatening to cancel what they term "these unofficial elections."

Indicative of the malaise was the resignation of Dariush Foruhur, one of the government's top negotiators on the Kurdish problem. He said he quit because of vote-rigging.

In a follow-up to his public declaration, Bani-Sadr also issued an order to the election supervisory council demanding that every voting station deal with the "many" complaints separately. The president also ordered the council to publish the total number of votes cast area by area on a daily basis.