Rebellion broke out today on a tiny Caribbean island in the nearby Grenadines group and armed police were sent from the main island here to crush it, police here said.

A government spokesman said Milton Cato, who was reelected prime minister of St. Vincent and the Grenadines on Wednesday, was swearing in an emergency Cabinet to deal with the crisis on Union Island, 45 miles south of St. Vincent.

Cato declared a state of emergency tonight and ordered a curfew in St. Vincent and other islands in the group.

Some 40 police armed with rifles and submachine guns were flown to Union after nearby Barbados flew 50 police here to keep up local security.

A police spokesman said a handful of rebels seized the Union Island airport and police station and were believed to be led by a man named Bumba -- by one account a member of the Rastafarian sect -- who came to the Grenadines from New York. The police apparently retook the airport.

Cato also appealed for assistance from the United States and to Britain, which granted independence to the east Caribbean state in October. [The State Department confirmed receipt of the request through the U.S. EMBASSY in Barbados and said it was under study.]

Union Island has about 4,000 of St. Vincent's total population of about 120,000.

Last Wednesday's election gave Cato's conservative and Western-oriented Labor Party overwhelming endorsement. It won 11 seats in Parliament out of 13 with the two opposition seats going to James Mitchell of the New Democratic Party, which has also been Western-oriented.

The United People's Movement, a leftist coalition whose leaders have expressed admiration for Grenada's new leftist prime minister, Maurice Bishop, did not win any seats. A Grenadan official denied any role of his country in the uprising.

Grenada's new revolutionary government has stirred controversy in the region by forging close ties with Cuba, keeping scores of opponents in jail, building an army estimated at about 1,500 by Western sources, and strongly criticizing the United States and its Caribbean policies.

On the day after St. Vincent became independent, Cato announced his country would build no army because it was too small, but might seek treaty arrangements to guarantee its security and would rely on its police to keep the peace.