A left-leaning opposition group claimed control of the Caribbean spice island of Grenada early yesterday morning following an apparent coup against the government of Prime Minister Sir Eric Gairy.

Sources said Gairy, 57, who has run the former British colony for 18 years and is best known for his flamboyant life style and United Nations speeches on behalf of flying saucers, is in New York. He arrived there Monday and has asked U.S. aid in putting down the rebellion, the sources said.

One administration source said Gairy had been given "a vague response" and that for the moment "we're just trying to figure out what the facts are."

The coup was announced by radio from Grenada, monitored in neighboring Barbados. The announcements were interspersed with reggae music. Maurice Bishop, 35, leader of the leftist opposition New Jewel Movement, proclaimed himself prime minister of a "new revolutionary government."

Additional information was scant, since telephone and airline links to the 133-square-mile island had been shut down. While Bishop and other speakers called the coup "bloodless," other broadcasts appealed for local doctors to help the wounded. The main police station was reported taken but pockets of resistance were still reported at mid-afternoon.

The broadcasts said that some 100 captives had been taken, including Cabinet ministers "arrested in their beds" but said they would not be harmed unless they resisted violently.

Located in the southern Caribbean, Grenada has a population of 100,000. Gairy, a former cane cutter and school teacher, began a labor and political movement during the early 1960s.

Although the British dismissed him from local office in 1961 for "misuse of funds," he quickly rallied support and became Grenada's political patriarch. He remained in power as prime minister following independence in 1974.

The New Jewel Movement first led organized opposition against Gairy at that time. Street demonstrations resulted in a shutdown of the island for nearly a month, as well as ax-handle beatings of dissidents and the police shooting of Bishop's father.

Although a Gairy-appointed investigatory commission later found the government guilty in the incidents, no official action was taken.

During 1976 elections, when a Jewel-led alliance won six of the 15 legislative seats, and in June, 1977, when the Jewels organized a peaceful demonstration during a Grenada meeting of the Organization of American States General Assembly, opposition activities were disrupted by government troops.

In a 1977 interview, Bishop described the Jewel movement as nationalist and socialist-leaning, along the lines of the governments of Jamaica and Tanzania. He said he had conferred with leaders in Jamaica, Cuba and elsewhere.

Bishop accused Gairy of putting island money in his own pockets and denounced alliances with rightest governments such as that of Chile, with which Gairy signed a mutual defense and military training pact.

The investigation of the Guyana mass murder last November indicated that Jonestown officials had considered moving the cult headquarters to Grenada.

In telephone interviews with news agancies yesterday, Gairy called the rebels a "little group of communists" and insisted that he maintained control of the government.

The United States does not maintain an embassy in Grenada, but sources said a political officer stationed in Barbados arrived in Grenada Monday on a routine tour.

The State Department said about 1,200 Americans visiting or living in Grenada were in no apparent danger and St. George's, the capital, was believed quiet.

Among the American residents are about 700 students at the St. George's Medical school, directed by the father of President Carter's former health adviser, Peter Bourne.