Iran's revolutionary authorities claimed an overwhelming victory today for their new Islamic constitution, but there was growing evidence that large segments of the population boycotted last weekend's voting as a measure of protest.

Officials of the ruling Revolutionary Council said only that a handful of voters across the country opposed the new constitution, which gives Ayatollah Ruhollah Khomeini legal control of the country and puts sweeping powers in the hands of the Islamic clergy.

With the vote over, diplomats hoped that the prospects for the hostages at the U.S. embassy would improve, since they no longer would be used as instruments of Khomeini's effort to consolidate the power of the Islamic clergy.

The officials said the two-day referendum drew an even larger turnout than the March vote that created the Islamic Republic of Iran. Final results are not expected until later this week.

Despite the reports of support for Khomeini, however, there were reports here that large numbers of voters stayed away from the polls in Kurdistan, Azerbaijan and Baluchistan, the three key provinces where most of the national minorities who make up half of Iran's population are congregated. t

Adding weight to those indications, Interior Ministry supervisor Hogatolesalan Hashemi Rafsanjani, a member of the Revolutionary Council, said residents in those areas "misused our tolerance" by trying to disrupt the referendum.

Many of them also were reported to have boycotted the vote last March.

Leaders of the various national groups opposed the constitution because it did not give them the degree of autonomy they sought and instead, gave power to the religious hierarchy in Tehran and the holy city of Qom, where Khomeini lives.

There has been steady and active resistance to Tehran's control among the Kurds and observers say that a spread of this sentiment could lead ultimately to a breakup of the Iranian nation. One of the more restive minority groups is the ethnic Arab population in Iran's oil-producing regions.

Foreign Minister Sadegh Ghotbzadeh was reported in an interview with the French newspaper Le Figaro to have said that the hostages will definitely be put on trial, and that they will be judged by the student captors.

While Pars, the official Iranian news agency, quoted the Figaro account today, the television news report here omitted, perhaps significantly, its most controversial section -- that the trial would be conducted by the students.

Moreover, the students themselves reiterated to reporters tonight that they do not intend to conduct the trial but rather plan to turn the hostages over to the country's Islamic judicial authorities. Iranian officials have never mentioned a date for the trial.

While analysts looked at the referendum more for its impact on Iran's internal political future, some diplomatic observers here and in neighboring countries suggested that an overwhelming vote for Khomeini could make it easier for Iran to negotiate the release of the 50 Americans who have been held hostage in the U.S. Embassy here for the past month.

A Khomeini victory, said one diplomat, might ease the pressures on the 70-year-old Shiite religious leader and possibly make it easier for him to order the radical student group holding the hostages to release them.

According to the newspaper Bamdat, Khomeini got that overwhelming victory. Not mentioning reports of defections in the three provinces where the national minorities live, the paper said many of the voters kissed their ballots marked "yes" and considered it to be supporting Khomeini against U.s. President Carter. Other voters dabbed their ballots with their own blood.

Meanwhile, informed sources here reported that Iran will send a low-level delegation to the International Court of Justice at the Hague, which has agreed to consider charges by the United States that Iran has violated international law by holding diplomats as hostages.

Authorities here indicated today that they are sending the delegation because Iran could lose the case by default if it does not offer some defense. b

The Iranians have refused to send a special representative to the U.n. Security Council debate on the hostages, but it is represented there by its permanent delegation.

The possibility that Iranian authorities would try the American hostages on spying charges remained unsettled today amid reports that former acting foreign minister Abol Hassan BaniSadr told students occupying the U.S. embassy that holding the diplomats hostage violates both international and Islamic law.

Although Bahi-Sadr broke no new ground in reiterating his well-known arguments regarding the hostages, he was the first Revolutionary Council member known to have made such arguments directly to several hundred students.

According to reports of the Monday meeting circulating here, he told the students he was against trying the American diplomats as spies because as official representatives of their country in Tehran they are protected by international treaties.

"The Koran teaches us that even agreements reached with infidels are sacred. It is question of Islam's very honor," Bani-Sadr was reported to have told the students.