This island nation recently seems to have done just about everything right that a developing country could from the Reagan administration's point of view, a kind of flagship in the Caribbean.

But if it is not sinking, it is not sailing either, and the main thing keeping it afloat is precisely the kind of massive direct aid that Washington tries to deemphasize.

A year ago, Jamaicans voted out a socialist government friendly to Cuba and replaced it with a hard-nosed, relatively conservative government backed by and sympathetic to businessmen.

The new government of Prime Minister Edward Seaga courts foreign investors. It came to power offering "deliverance" from socialism with repeated promises to put the country's economic house in order.

Seaga was welcomed in January as the first state visitor to the Reagan White House.

"We feel strongly," Secretary of State Alexander M. Haig Jr. said then, "that the future of Jamaica is not only of vital importance in its own right but also as an example for the entire Caribbean basin, a region where so many newly formed nations and peoples are facing the alternatives of authoritarian solutions and economic determinism, or a market economy and democratic process. We are all vitally concerned that Jamaica succeed."

The leftist government of former prime minister Michael Manley combined an apparent hostility to the private sector, with chaotic economic management and radical rhetoric, and it devastated Jamaica's economy with seven consecutive years of negative economic growth.

The Seaga government predicts that 1981 will see a 1 percent growth in the gross domestic product. According to the government's survey released in June, the hitherto growing number of unemployed dropped from 27.9 percent in April 1980 to 26.8 percent in April 1981. But a foreign economist estimated that the economic growth will finish up the year "probably closer to zero percent and could be negative again."

A July report by the U.S. Embassy noted that the reason for "apparent improvement" in the unemployment situation "was an increase in underemployment -- employment in activities such as street-side selling or casual farm work, which occupy a person only a few hours a week but yet get the individual recorded as employed in official labor surveys."

The Seaga government made clear from the start that it would need to borrow heavily to revive the economy, but Seaga promised his first year in office would be one of "dynamic change and momentum."

According to a U.S. Embassy report, financial support from the International Monetary Fund, refinancing and new credits from foreign commercial banks, pledges of support from multilateral financial institutions and from bilateral donors such as the United States "will total over $800 million in this government's current fiscal year."

A Western econmomist puts the figure closer to $1 billion, or about 30 percent of the gross domestic product. Of the shrinking U.S. aid program, $100 million is earmarked for Jamaica this year and another $60 million in governmental aid is coming from Venezuela. The IMF has made $300 million available this year.

The Reagan administration helped form an American business committee on Jamaica headed by David Rockefeller and two dozen chief executives of major corporations. Partly because of the committee, Jamaica has registered 470 investment proposals, the vast majority of the foreign ones being from the United States.

But only 21 projects are currently in production, with a total capital investment of $43 million, according to statistics from Jamaica National Internal Promotions, the organization set up by Seaga to facilitate private investment. Another 398 projects have not passed the stage of preliminary inquiries and opening of files.

If all the projects were realized, the total direct investment would be about $777 million, but the total number of jobs created directly would be about 37,000 in a population of 2.2 million, with 250,000 unemployed or underemployed.

"It takes time to turn a train around in its tracks. But the mood has changed so much in a year," said Trevor Boothe, a director of investment promotions. "A lot of the larger projects which would have potential for significantly improving employment are the ones that take the longest to get in place."

But local economists, even those close to the Seaga government such as consultant Paul Chen-Young, are worried.

"An investment has to be really attractive in Jamaica to compensate for interest rates in the United States," said Chen-Young. "You need to have double those rates on return on investment to compensate the risk."

One conservative local economist, who asked not to be named, analyzed the situation this way:

"Here you've committed yourself to a private sector strategy. The U.S. and business are committed and giving strong support but the government cannot say, 'You must invest in Jamaica.' So there is this gap, and if it is not supplemented by official flows, the strategy is going to fail."

Although the palpable tension of last year's elections and much of the political violence that shook the country and made tourists stay away has dissipated, the tourists are still staying away.

Manley, meanwhile, is again climbing in opinion polls. After losing 51 of the parliament's 60 seats to Seaga's party last year, Manley's personal popularity rating is now higher than Seaga's.

"Everything has become, what is the U.S. doing for us?" said Manley. "There is a sort of tremendous reversal of any attempt to develop the psychology of self-reliance."

Businessmen and members of Seaga's government deny this, but many, like Boothe, question whether Jamaica is an example for others.

"What is being done here," said Boothe, who was formerly with the United Nations, "I do not believe can be done anywhere else. This is a special case." Boothe, like other Jamaicans, said he believed Jamaica is being rewarded by Washington for pursuing democracy and free enterprise. "Of course," he added, "there may be some countries that do not like this."