The State Department yesterday denied reports from two Caribbean leaders that unidentified U.S. officials had suggested to Grenada's neighbors weeks ago that the United States would be willing to mount a military operation against the island.

But a department spokesman acknowledged that the first "urgent approach" from eastern Caribbean countries to discuss options on Grenada was made Oct. 15, four days before the execution of Prime Minister Maurice Bishop and most of his cabinet and before the leaders of the coup imposed an around-the-clock curfew with orders to "shoot to kill" violators.

Secretary of State George P. Shultz had said earlier in the week that the United States did not begin to develop plans to invade Grenada until last Thursday, Oct. 20, after the executions in Grenada prompted concerns about the safety of 1,000 U.S. citizens on the island.

Shultz said the Oct. 20 meeting, chaired by Vice President Bush, was called "to review the grave turn of events and to consider their implications for the American citizens on the island."

State Department spokesman Alan Romberg told reporters yesterday that he had no details about the earlier "urgent approach" from some Caribbean leaders. By evening, however, the department issued a statement saying the "informal approaches . . . took the form of Caribbean leaders relaying to us through normal diplomatic channels their increasing concerns and apprehensions about the breakdown of order and growing violence and their belief that direct action might be necessary to prevent more deaths by a tyrannical, illegal government."

The statement did not address the fact that there had been no deaths by Oct. 15, the date Romberg said the initial contacts were made. Bishop was under house arrest at the time and no curfew existed on the island.

Asked about the discrepancy, Romberg amended the statement to say the regional leaders were concerned about the "breakdown of order and, after Oct. 19, growing violence" and the possibility of more deaths.

In a televised address last night, President Reagan did not mention the earlier diplomatic discussions between U.S. and Caribbean officials. Reagan said he learned about the "urgent request" for U.S. intervention "last weekend when I was awakened in the early morning hours . . . ."

But in the State Department briefing, Romberg disclosed that the United States "had been informally approached on an urgent basis by the Caribbean states as early as the weekend of Oct. 15th and 16th, after the takeover by the Revolutionary Military Council on the 13th."

The new information about the pre-invasion exchanges between U.S. officials and Caribbean leaders raises questions about the official rationale given by Reagan and his senior advisers for the assault on the island. Tuesday morning, in announcing the invasion, Reagan said the bloody purge of Bishop's rule persuaded the United States that "American lives are at stake."

The State Department denied that the United States "stimulated a request" from Grenada's Caribbean neighbors for an invasion force. "That simply is not the case," Romberg said.

Washington Post correspondent Don Oberdorfer, traveling with Shultz yesterday, reported that the secretary vigorously rejected any suggestion that the United States had sought a pretext to invade Grenada.

"We haven't been trying to gin up anything," Shultz said. "We've been worried about American citizens there and particularly so when we see all of this violence that has taken place and the lack of any credible government."

In a speech Wednesday night, Thomas Adams, prime minister of Barbados, said a military aide in his government was approached by an unidentified U.S. official on Oct. 15 who offered U.S. assistance to provide transport for a military force to go into Grenada and free Bishop, who was under house arrest by Grenada's military leaders.

Also on Wednesday, a senior official in Jamaica's government told Washington Post correspondent Juan Williams that unidentified U.S. officials had been seeking for several months to have the Caribbean Common Market (CARICOM) nations "isolate" Grenada as a "communist outpost" and had urged the regional governments to consider military action against Grenada.

Last evening, State Department officials did not specifically address the statements by these officials, but a spokesman said "we believe this statement refutes that."

The statement said that at no time during the invasion-planning process "did the U.S. commit itself to military involvement" before President Reagan gave a tentative go-ahead on Sunday.

When Romberg was pressed at the noon State Department briefing on whether he was "positive that no American official" had suggested some kind of military operation against Grenada to Caribbean leaders, Romberg said he would "try to get a formal answer" from top department officials.

Also yesterday, Prime Minister John Compton of St. Lucia, one of the eastern Caribbean countries that has participated in the invasion, told reporters at the White House after meeting with Reagan that the main reason for requesting U.S. assistance was the Cuban military buildup on Grenada. "The United States came to our aid because we thought the Cuban military buildup was threatening the whole of the southern Caribbean," he said.

Compton said that Barbados and the OECS states met Oct. 20 and decided to request U.S. assistance. They then tried to persuade the 13-nation CARICOM countries to endorse the plan, he said.

However, reports from news services in the region over the weekend indicated that the CARICOM membership refused to go along with armed intervention on Grenada, leaving the eastern Caribbean group to act on its own with Jamaica and Barbados.

"The letter of request was delivered to the American Embassy on Barbados on Sunday," Compton said.

In the meantime, U.S. intelligence sources said, word of the invasion proposal leaked out from the CARICOM and OECS meetings, complicating efforts by U.S. diplomatic officials to negotiate the evacuation of U.S. citizens on the island. "The Cubans had the whole story" during the weekend, one intelligence source said.

As a result, intelligence officials monitored the arrival in Grenada last Sunday or Monday of at least one Cuban transport plane carrying military officials, reinforcements and munitions for the detachment of about 600 Cuban construction workers who have been building a 9,000-foot airport runway at Port Salines on the island's southern end.