For a few hours on Thursday this tiny island will recapture the place in the world spotlight it held with intensity in the early 1980s.

When President Reagan's speech at a summit meeting of Caribbean leaders is over and the White House party flies away, however, Grenada's 94,000 inhabitants will be left again with a set of intractable problems, much like those of their neighbors all along the somnolent Windward Islands chain.

High unemployment, poor roads, faulty electricity and telephone systems -- these all were problems that existed when Maurice Bishop and the New Jewel Movement seized control in March 1979. Despite a fever of Marxist rhetoric, they were still problems when Bishop's revolution degenerated into a bloody power struggle in October 1983, leading U.S. forces to invade and set up a government friendly to Washington.

There was much promise and excitement that an infusion of U.S. dollars would alter the island's economic fortunes just as U.S. troops had changed its political fate, sentiments fed by officials in Washington and the U.S. Embassy here who strongly promoted hopes of swift economic improvement, particularly through investment by American businessmen.

Acting on its own pitch, the administration brought 21 businessmen to the island on an investment promotion tour within months of the invasion.

Two years and four months later, only two U.S. investments have gone into the record. The first, a tiny spice-packing factory, has gone bankrupt.

The second, a wooden toy factory, closed four months after it opened and its owner, William Ingle, pleaded guilty last December in Norfolk, Va., to defrauding the eager U.S. government out of $350,000. He was sentenced last week to serve two years in prison and pay a $10,000 fine and more than $121,000 restitution.

Other U.S. companies, including Johnson & Johnson, have expressed interest in starting up projects later. But enough potential investors have dropped back from previous plans that the U.S. government now says its investment list is confidential.

The one truly visible change here since the invasion is Point Salines International Airport, which Prime Minister Herbert Blaize inaugurated Monday. Although Reagan and other arriving passengers can now see only a shiny new facility, the Cuban-constructed airport was the most prominent symbol of revolutionary activity in St. George's and heated concern in Washington in the weeks and months before the 1983 invasion.

Blaize, who was elected with U.S. blessings in December 1984, carried on the tradition in a news conference yesterday with foreign reporters here for the presidential visit. He said Reagan was right to fear that Cuba and the Soviet Union would have used the airport for military purposes. To prove his point, he called attention to the facility's large kitchen.

Although Blaize did not explain, he presumably meant the airport would have been used to feed Communist soldiers in transit on their way to somewhere if U.S. forces had not stepped in.

Reagan, voicing concern soon after he took office, previously had denounced the size of the runway rather than the kitchen. At 9,000 feet, he said in a televised speech four years ago, the runway was too long for commercial needs and betrayed the military intentions Bishop and his Cuban allies had in mind.

Those concerns seem abated now that the United States has become the island's unchallenged patron and U.S. charge d'affaires Roy Haverkamp has hung a poster behind his embassy desk reading: "Under new management."

The State Department reference guide for Reagan's visit points out that the runway, roughly the same length as those of neighboring islands, "easily accommodates wide-bodied jet aircraft, including the Boeing 747."

Except for a handful of followers of Bishop, the U.S. invasion remains a popular memory among most Grenadians.

"Getting rid of the Revolutionary Military Council was something the people saw as being in their interests," said George Louison, Bishop's agriculture minister, who resisted when a hard-line Marxist faction killed Bishop and established the council.

U.S. aid, amounting to $72.6 million in fiscal years 1984 and 1985, has become a mainstay of the economy here since then, although U.S. officials warned from the beginning that popular expectations were too high and that promised U.S. aid levels would have to drop. Diplomats are now banking on $14 million for fiscal 1986, less than half the previous years' rates.

Nevertheless, for the first time in decades motorists can drive normally around St. George's because U.S. money has paid for resurfacing the roads. With another injection of U.S. funds, the Blaize government has met debt payments and ministry payrolls despite low income from such traditional revenue sources as agricultural exports and tourism.

Other indices are not as promising. Tourism, although up sharply, still produces a hotel occupancy rate of only 41 percent. Unemployment is estimated at between 20 and 34 percent, compared to a 12 percent level claimed by the Bishop government in its last year.

"People are not happy," said Leonard Alexander, a government employe. "On the surface, it looks good but people are looking for more movement. The government is moving too slow."

For many, the main complaint is scarcity of jobs, particularly for young men and women who were the revolutionary government's natural constituency before October 1983.

"They just get a few jobs when the queen of England comes, or President Reagan, something like that, and then when it's over they won't have jobs again," said one young man, referring to the queen's visit here last year.

Blaize dismissed such talk as the complaints of "a tiny minority who spread malice and discontent."