Terrorists set fire to a crowded movie theater in the Iranian oil port city of Abadan Saturday night, killing at least 377 people in one of the worst disasters of its kind in history.

Information Minister Dariush Homayoun said the fire appeared to be one of a series violent antigovernment acts committed by "fanatics" and directed against "all signs of modern living and Westernization in Iran."

Some diplomats held out the possibility that it could also mark the resurgence of terrorism by the Mujaheddine (People's Strugglers), the most active of the hard-core urban guerrilla groups that were responsible for numerous bombings and assassinations in Iran a few years ago.

The country's official news agency, reporting the fire yesterday about 13 hours after it happened, blamed "saboteurs" and "unidentified protesters" who it said not only doused the theater with gasoline but also "set fires on all four sides of the building to prevent rescue attempts."

Tehran newspapers said about half the audience managed to get out, an estimated 100 escaping unhurt and 223 suffering burns or other injuries. The rest were trampled to death, asphyxiated or burned alive.

Prime Minister Jamshid Amouzegar called the fire a "national catastrophe" and the shah sent his condolences to families of the victims. Cinema owners in Tehran and several provincial cities closed their theaters in protest, and "backlash" demonstrations were reported in Abadan and other towns in southern Iran.

Although the government refused to speculate about the exact identity of those responsible, angry demonstrators were said to blame extremist Moslem reactionaries whom authorities have accused of inciting widespread antigovernment riots this year. The shah recently charged that "the rioters receive their orders from the Communists," but no evidence of such involvement has yet been produced.

The official Radio Iran described the perpetrators as "terrorists" and quoted the Abadan police chief as saying a number of suspects have been arrested. No other details were given. Newspapers earlier reported that the manager of the theater and a janitor, who was reportedly found in a "drunken state," were detained.

No one claimed responsibility for the fire.

The prominent Iranian opposition leaders - Ayatollah Shariat Madari, the Shiite Moslem spiritual head, and Mosen Pezeshkpur, a leading nationalist figure in parliament - denied any responsibility and denounced those who cause it. Madari blamed "hotheaded people with whom we have no links whatsoever."

Since Ramadan, the Moslem month of fasting and prayer, began Aug. 8, extremist religious leaders have been addressing mass rallies throughout Iran urging Iranians to attend prayer sessions at mosques instead of watching movies or television.

In the hours following the Abadan fire, another movie theater and a restaurant were firebombed in the southern Iranian city of Shiraz, injuring three people, and a restaurant in Tehran was set afire. Two days ago a theater in the northeastern city of Mashad was burned down, killing three people sleeping there. Earlier a bomb was placed in a Persian restaurant in Tehran, killing one person and injuring 40 others, including 10 Americans.

All these incidents came after a series of rampages by religious demonstrators in a dozen cities. At least 15 people were killed when police and troops opened fire on unruly crowds and martial law was imposed on the central city of Isfahan - home for about 12,000 Americans, mostly defense contract personnel, and the site for major industrialization projects.

There was speculation that the burning of the theater may have been timed to coincide with the 25th anniversary of that CIA-backed coup that returned the shah to power in 1953 after a brief exile. The government organized pro-shah rallies in several cities Saturday to mark the anniversary.

Witnesses reported that many of the victims of the fire were women and children. About 10,000 foreigners, including many Americans, live in Abadan but police said none was believed to be in the theater, which was in a poorer, working class district of the city.

Flames and smoke suddenly swept through the movie hall around 10 p.m. as an audience of about 700 watched an Iranian family film called "Reindeer" at the Rex theater. According to press accounts from the scene, panic-stricken filmgoers stampeded toward the building's two emergency exits, which reportedly had been locked as an anti-terrorist measure.

Screams filled the night as hundreds of bystanders gathered helplessly outside, unable to enter the inferno to rescue victims.

Most of the bodies were charred beyond recognition. Some determined searchers tried to identify relatives by their rings or other jewelry.

Rescue workers gagged at the grisly scene and women wailed in the streets.Bulldozers plowed mass graves - normally banned by Islamic custom - and merchants donated yards of white cloth to make shrouds for the dead.

Firemen battled the blaze for six hours before bringing it under control. At first they were unable to get within 50 yards of the theater because of the searing heat, and when they eventually put out the flames, nothing was left of the building but twisted and blackened steel girders.

Moderate opposition political leaders in Tehran repudiated the terrorism, and some suggested cynically it might be part of a government plot to recoup support among an increasingly critical public.

"It was really an abominable act," said long-time dissident Karim Sanjabi, 73. "The whole country is grief-stricken."

"I think it's a government intrigue to show foreigners that Iran is unable to have a democratic system," another dissident said.

The fire was one of the worst of its kind in the last hundred years. In 1881, 850 people were killed in a theater fire in Vienna, and six years later 200 died at the Opera Comique in Paris.

Three of the worst fires of this century have been in the United States. Chicago's Iroquois Theater burned in 1903 with a loss of 602 lives. The Coconut Grove nightclub fire in Boston killed 491 in 1942, and on May 28, 1977, 164 died in a fire at the Beverly Hills Supper Club in Southgate, Ky.