Fighting between Moslem fundamentalists and leftists marred two May Day demonstrations today in Tehran after a number of bombs were reportedly discovered and defused along one of the parade routes.

The ruling Revolutionary Council, meanwhile, said Iran would refuse to negotiate with the attackers holding Iranian diplomats hostage at Iran's embassy in London.

The statements coincided with a warning reported here by Foreign Minister Sadegh Ghotbzadeh that if any of the Iranian hostages were harmed, those Arab Iranian prisoners whose release the captors were seeking would be "tried and executed."

Echoing the sentiments of Ghotbzadeh, who is traveling in the Persian Gulf, a Foreign Ministry spokesman here said that if the captors in London carried out their threat to blow up the embassy and kill the hostages, Iran would expedite the trials of the 91 prisoners jailed in the oil-producing province of Khuzestan. The statement indicated that the Iranian Arabs, accused of various acts of sabotage in their fight for regional autonomy, were being held without trial.

The spokesman denounced reports that some Iranians planned to occupy the British Embassy here in retaliation for the seizure of the Iranian Embassy in London. The spokesman said these rumors were provoked by the United States and Iraq to discredit Iran, and he said the population was being urged to remain calm about the London embassy takeover.

It was not immediately clear whether the shooting of a British secretary working for the Anglican bishop here was related to the events in London. The British woman was reported seriously wounded.

In today's demonstration, tens of thousands of Iranians marched toward the occupied U.S. Embassy shouting slogans such as "Death to America, enemy of the oppressed" and "Islam is victorious, America is destroyed."

The marchers gathered at the embassy after several bombs had been discovered attached to an overpass along the march route. The bombs were defused, according to Iranian news media.

In a speech to the crowd in front of the embassy, a leading Iranian clergyman blamed the attempted bombings and a rash of explosions in Tehran in the past several days on the United States. He said that leftists working on behalf of the United States were responsible for shooting incidents at the embassy for the past three nights. Last night one Revolutionary Guard posted outside the compound was reported wounded by gunfire from a passing car. p

A representative of Iranian workers read a communique at the rally demanding the return of the deposed shah, condemning Friday's U.S. hostage rescue attempt and calling on American workers to rise against President Carter.

Two other demonstrations by leftist groups broke up into fighting with Moslem fundamentalists at two other points in the capital. At Azadi Square west of the city, a number of persons were injured when about 3,000 rightists tried to disrupt a rally held by more than 20,000 supporters of the Marxist Fedayan guerrilla group.

The rightists, who shouted slogans such as "Death to communism," were beaten by a larger crowd of leftists.

In south Tehran, a rally by the radical Islamic Mujaheddin guerrilla group was attacked by Moslem fundamentalists loyal to Ayatollah Ruhollah Khomeini and serious fighting ensued. There was no immediate estimate of the number of casualties.

The fighting forced rally leaders to discontinue their speeches and call off the meeting.