Pentagon officials yesterday disclosed that they have reduced their estimate of the number of Cubans in Grenada from 1,100 to between 700 and 750, meaning that now the U.S. invasion force there is contending with only "snipers and stragglers."

Meanwhile, in a briefing tonight at the airport in Bridgetown, Barbados, Vice Admiral Joseph Metcalf III, the operational commander in Grenada, said that a U.S. "scouting action" had begun tonight on the island of Carriacou, a Grenadan possession less than 20 miles north in the eastern Caribbean Sea.

Metcalf acknowledged reports of resisting forces still on Carriacou but said that he had no firm information on what the party was likely to find.

The admiral commanding the U.S. force of more than 5,000 soldiers in Grenada said Friday that several hundred Cubans had escaped into Grenada's hills and could cause problems for U.S. troops in the coming weeks.

Cuban prisoners will be repatriated under a U.S.-Cuban agreement, announced by Havana last night. Details on page A8.

The new, lower estimate of Cubans, which conforms to the number that Havana has consistently claimed were in Grenada, means most of the Cuban opposition has been accounted for, since at least 638 were captured and officials have said dozens were killed.

Administration officials had used the larger number as evidence of Havana's intention to occupy Grenada and turn it into what President Reagan called a "military bastion." Without retreating from their broad assessment of Cuban intentions, Pentagon officials said yesterday that a closer reading of captured documents had caused them to change their estimate.

They said that they could not predict last night what effect the new estimate will have on the length of stay of the U.S. Army, which they continued to say will be "as short as possible."

However, administration officials said that they believe Cuban soldiers still are manning antiaircraft guns and other "defensive positions" on Carriacou. The island is 13 miles square miles and has a population of about 6,000.

Washington Post correspondent Edward Cody, who spent 14 hours on the island the night before the invasion of Grenada, reported seeing no apparent military installations on the smaller island, nor Grenadan or Cuban military personnel, nor anyone carrying arms.

But one administration official said, "There are Cubans on that island. They do have antiaircraft positions. They have prepared defensive positions around the airfield."

Earlier in the day, the Cuban ambassador to Barbados told reporters that 784 Cubans are on Grenada, 22 of them military advisers. He said reports that Cubans are still fighting U.S. forces there are "absurd."

Pentagon officials said that sporadic fighting continued in Grenada yesterday, with a Marine helicopter encountering antiaircraft fire and ground patrols running into snipers. Army Rangers began pulling out Friday night, and about 500 Marines were said to be returning to their ships yesterday. But more than 5,000 soldiers from the Army's 82nd Airborne Division remained on the island yesterday.

The U.S. Agency for International Development, meanwhile, began airlifting food and other supplies to Grenada because of shortages that have developed on the Caribbean island since U.S. forces invaded, administration officials said.

A senior official who asked not to be identified said that the supplies are intended primarily for hundreds of civilians who have been forced from their homes by the fighting. Other officials said that they are concerned about general food and water shortages that are affecting even civilians not displaced by the hostilities.

The United States launched its surprise invasion of Grenada, which has a population of 110,000, on Tuesday, saying about 1,000 U.S. citizens there had been endangered by a coup the week before. U.S. officials also said that they were responding to requests from neighboring Caribbean countries to end the turmoil in Grenada and replace its leftist government with "democratic rule."

Pentagon officials said yesterday that Grenada will be "opened up" to reporters for the first time today, with 100 correspondents flown in each morning and allowed to wander without military escorts.

Under orders from the Joint Chiefs of Staff, no reporters were permitted in Grenada during the first two days of the invasion. Since then small groups have been flown in and out for guided afternoon tours.

The debate sparked by the administration's handling of news coverage of the invasion continued in the Senate yesterday, where lawmakers voted, 53-to-18, for an end to restrictions on news coverage. The vote came on an amendment to the debt ceiling bill, but it will be reconsidered Monday because some senators said that they thought it was too sweeping.

"You could have reporters from Tass," said Sen. John G. Tower (R-Tex.). "Is that what you want?"

Senate Minority Leader Robert C. Byrd (D-W.Va.) yesterday called for a bipartisan congressional fact-finding mission to Grenada because of what he called the administration's sharp restrictions on information about the invasion.

"We're not getting all the facts in the beginning, and we're not getting all the facts now," Byrd told reporters. "I think what we are getting is censored news . . . a little morsel at a time."

Byrd also criticized a lack of consultations with Congress over the invasion and said he wanted the inquiry to focus on the adequacy of U.S. intelligence in the Grenada invasion.

Majority Leader Howard H. Baker Jr. (R-Tenn.) said that such a fact-finding mission is "a good idea" and that he might join Byrd in leading it. A resolution to authorize such a mission was being drawn up by Byrd's staff yesterday and was expected to reach the floor Monday, but Baker's aides said later that he has not yet signed off on the proposal.

Administration officials said in interviews this week that it was decided in the early stages of planning to allow the Pentagon to handle the dissemination of information on its own terms, and also set the rules for news coverage of the invasion. They said this was part of Reagan's larger delegation of almost all aspects of the invasion to the military.

"The planning of the entire thing was left to the Joint Chiefs of Staff," said an administration official. "Their attitude tends to be that the press makes it hard to fight wars."

Many officials within the Pentagon, especially public information officers, were also frustrated with the ground rules, which most of them attributed to Gen. John W. Vessey Jr., chairman of the Joint Chiefs. "I've never seen it clamped so tight," one said.

White House officials apparently decided on Oct. 23 that they would keep to themselves the job of informing the Congress about the invasion but that the Pentagon would channel details to the public.

This control over the information was what military officials wanted, and top presidential aides, including chief of staff James A. Baker III, apparently offered no objections.

Baker essentially froze out the chief presidential spokesman, Larry Speakes, and communications director David R. Gergen from advance information about the invasion.

Officials said this decision set the tone for the week and had the larger effect of giving the president's chief spokesmen a secondary role in determining how the administration would present one of the major foreign policy initiatives of the Reagan presidency.

Pentagon officials released a few more details about the invasion yesterday, including a new casualty count of 76 U.S. servicemen wounded in action. The number of U.S. troops killed remained at 11, and there were still seven missing.

Pentagon officials said they had no firm count of Cuban casualties. Metcalf said that 70 opposing soldiers have been killed, but he said he does not know how many were Cuban and how many were Grenadan.

U.S. officials said they arrived at their earlier estimate of 1,100 Cubans on the island by interrogating captured Cubans. Havana said most of those Cubans are construction workers, while U.S. officials said they are soldiers "impersonating" construction workers or else the equivalent of U.S. Army engineering battalions, trained both to build and to fight.

During the afternoon, Pentagon spokesmen said that Marines and Army troops were continuing to encounter sporadic shooting and antiaircraft fire.

"I know of no pitched battles being fought now, but neither is anyone declaring victory," one official said. "I think there are some operations ahead of us."

By the end of the day, however, officials said that they believed only "snipers and stragglers" remained.

Nevertheless, they said it could take some time to clear the 133-square-mile island of resistance.

Metcalf had said earlier that it "is standard communist methodology to keep us off balance with snipers." He also said that the Grenadan army "collapsed . . . cut and run" early in the U.S. invasion and was unlikely to offer further organized resistance.

An American who visited Carriacou three years ago described it as a dry island, one-tenth the size of Grenada, that seemed to have more goats than people. He said about half the island was served by electricity, which worked sporadically.

The airport consisted of an unpaved strip, he said, and a shed with a sign, "Visitors please report to police station downtown with their passports." It could not be learned yesterday whether the strip has since been paved.

An administration official said the Cubans on Carriacou could not have left Grenada since the invasion began without being spotted.