The revolutionary leadership of Grenada, rejecting "imperialism" and "Westminster democracy," has moved to transform the traditional economics and politics of this Caribbean island in ways that increasingly are bringing it into confrontation with the United States.

At stake, as the Reagan administration presents the case, is whether the English-speaking Caribbean has its first Marxist dictatorship, allegedly disregarding civil liberties and, through alignment with Cuba and the Soviet Union, providing a platform for strategic inroads against U.S. security near crucial shipping lanes from the Atlantic to the Gulf of Mexico.

For Prime Minister Maurice Bishop and his followers, however, the question is whether a small nation in the southern shadow of the United States can choose its own friends internationally and follow its own path to development after three decades under an eccentric pro-western despot known for his interest in flying saucers.

Four years after Bishop's New JEWEL (Joint Endeavor for Welfare, Education and Liberation) movement seized power in the area's first armed coup, the answers are still incomplete. But, nudged along by a determinedly hostile attitude from the United States, Grenada's eager young leaders increasingly seem headed toward a state-dominated economy, authoritarian rule without elections and a Soviet-oriented foreign policy in collaboration with Cuba.

Private businessmen still run most of the island's import-based commerce, its most lucrative economic activity. But that is due to change. Future boundaries between government and private enterprise were defined in an investment code that went into effect last month. Reserving a wide range of economic activity for the state, it reflects an effort by the government to push businessmen out of traditional import-export merchandising into tourism or small industry.

Deputy Prime Minister Bernard Coard, who also is finance minister, said in an interview that this will end what he and Bishop call "invoice technology" that has been the main economic activity of the "old order" on this 133-square-mile island. The code provides for the government to move into infrastructure and most foreign trade while private capital gets incentives to invest in new tourist hotels or factories.

Several businessmen expressed doubt, however, about the ability and willingness of private capital to invest in industry on an island of 110,000 inhabitants surrounded by similar, more developed islands also trying to export for foreign exchange.

Tourism, they added, is a natural product for this beautiful island, but depends on economic conditions in Europe and the United States and political relations between Grenada's revolutionary government and other nations, particularly the United States. A new international airport due to be finished in mid-1984 will be a powerful stimulant, they said, but it alone will be insufficient if Grenada becomes known as another Cuba.

"I think people are willing to wait until the airport is finished and see over the next five years whether tourism will be allowed to flourish," said one of the island's most prominent businessmen. "If it's not, I think a lot of people are going to say they're not willing to devote their active years to building socialism, and they will begin to emigrate."

Coard, 38, an economist trained at Brandeis and Sussex universities, said he had a survey taken last month to see whether President Reagan's talk of Grenada as a security threat and Bishop's talk of a U.S.-sponsored invasion had hurt hotel occupancy. Not one reservation was canceled even at the height of the public recrimination, he said.

But Royston Hopkin, head of the Grenada Hotel Owners' Association, said that the hotels have been running at an annual occupancy rate of only 25 percent and that the political confrontation has indeed hurt business.

"This has affected us tremendously," he said. "Reagan identified us as a threat, and the next week our prime minister says there's going to be an invasion. That's bound to hurt tourism."

Coard acknowledged his government is walking a narrow line. But he said even amid U.S. hostility, Grenada can enjoy small-industry exports and increased tourism once the airport is finished because "only an infinitesimal percentage of the market" is necessary to make the difference on this small island.

"I know what we need to do," he added. "Whether we can really do it, that is what is going to determine our future."

A diplomat with close official contacts here said problems in putting policy into practice often stem from inexperience at the top of Bishop's government that revolutionary enthusiasm cannot make up for. In addition, he said, the government is short of qualified officials at lower levels.

"They have a country the size of a city, but they have the obligations of a state--embassies, United Nations, defense and so on," he added. "It's too much. They just don't have the material and human resources."

The revolutionary government's new style of politics centers on broad participation by citizens in discussions with local and national leaders conducted by a variety of mass organizations. Hailed by Bishop and his aides as a step forward in democratic participation, the system is derided by some Grenadians as "theater democracy" that never really puts into question basic decisions taken by the leadership.

"I went to one of the meetings once," said an older hotel owner, "but it was so ridiculous I just walked out." The system has imparted a Boy Scout-style zeal new to youthful Grenadians, however, and the government's surge of activity has reduced unemployment from nearly half the work force to about 14 percent, according to government counts. Young men with purposeful looks on their faces can been seen racing about most days instead of the traditional "liming," or hanging around.

Most important, critics say, the new style contains no provision for changing the leadership or voicing opposition to it. Bishop has pronounced parliamentary-style democracy "dead" for the island and closed private newspapers. He has promised to organize elections at an unspecified future date but refuses to be pinned down as to when.

Opposition to the government has landed several score persons in the prison looking down on St. George's postcard harbor from atop a steep hill. The prisoners, held without trial, used to number about 100; friends and relatives knew who they were. Now, according to Grenadians who try to keep track, many names are kept secret and no one knows how many prisoners are "up the hill."

One, Anthony Mitchell, a founding member of the New JEWEL movement, was released recently after entreaties from his mother. Mitchell, 32, said in an interview in Barbados that he was held without trial for "three years, one month and a day" on an order signed by Bishop saying he was "suspected" of antistate activities.

The United States has complained of the lack of elections and human rights abuses consistently in representations to Bishop's government, along with the island's warm relations with Cuba and the Soviet Union. The most recent exchange came two weeks ago in a meeting between James Emmanuel, the Foreign Ministry's permanent secretary, and Kenneth Kurze, political officer at the U.S. Embassy in Barbados that has Grenada as part of its territory.

Emmanuel, in an interview, said he repeated Grenada's frequent suggestion that Bishop meet with Reagan or that Secretary of State George P. Shultz meet with Foreign Minister Unison Whiteman for "dialogue."

The United States, however, has mounted a boycott of Bishop's government, refusing to accredit an ambassador to Grenada or accept Emmanuel's nomination as Grenada's ambassador to Washington.

In addition, the Reagan administration has left Grenada out of its proposed Caribbean Basin Initiative and sought to prevent loans to Bishop's government from Western Europe, the World Bank and the Caribbean Development Bank. Coard said the government also suspects that the CIA played a role in seven incidents of suspected sabotage over a six-week period in 1981.

Against that background, the government has become increasingly strident in its denunciations of U.S. actions. Shortly after Reagan called Grenada a threat to U.S. interests last month, Bishop countered by calling Reagan a "real, true-to-life fascist in the best traditions of Adolf Hitler and Nazi propagandist Joseph Goebbels," about to promote an invasion of the island.

In a reflection of Bishop's foreign-policy alignments, portraits of President Fidel Castro of Cuba; Daniel Ortega, the Nicaraguan junta leader; and Libyan leader Muammar Qaddafi decorate the entrance hall at Butler House, the hilltop hotel transformed into government headquarters.

The Soviet ambassador, Genadily Sazhnev, recently inaugurated service of Tass, the official Soviet news agency, to keep Butler House officials informed of world events. Sazhnev, a former officer at the Soviet Embassy in Havana, is regularly seen bumping along in a buff-colored Mercedes between town and his residence overlooking Grand Anse beach as it arcs gracefully away from the harbor. Cuba, Libya and Venezuela are the only other countries with ambassador-level representation here. Bishop last week visited North Korea, reportedly seeking aid there, too.