The Shiite captors of six Americans still held in Lebanon may release their remaining hostages if Kuwait agrees to free the two Lebanese Shiites imprisoned among 17 convicted terrorists, according to a well-placed Arab diplomatic source and relatives of the hostages.

There have been indications of such a compromise from the Shiite captors, who previously have demanded freedom for all 17 terrorists, according to the Arab source. The main obstacle to such a solution is Kuwait's refusal to negotiate release of any of the terrorists, the source added.

The source, whose country has served as an intermediary with the captors over the past year, said there were also "indications" that the Shiite captors are anxious for a way out of the impasse because of mounting Arab pressure, particularly from Syria, to free the remaining Americans.

The disclosure of a possible compromise appears likely to increase pressure on the United States and Kuwait to explore, directly or indirectly, some resolution of the hostage issue.

However, Kuwait's ambassador here, Sheikh Saud Nasir Sabah, denied that there were any talks under way on the hostage issue involving his government. He added in an interview Friday, "There is no way, or any possibility, of any kind of compromise."

The Rev. Benjamin Weir was freed Sept. 14 after 16 months' captivity bearing a message for President Reagan from his captors, who threatened to kidnap and possibly kill other Americans unless all 17 terrorists were freed. Weir said he saw four of the other American kidnaping victims before being released; the fate of the two others is unknown.

Weir's 27-year-old son, John, said yesterday that the idea of swapping the Americans for only the two Shiites in Kuwait was first presented to the administration early in the summer by the hostage families as one possible way to break the long deadlock.

John Weir said the proposal was based on "an educated guess" that Shiite fundamentalists in Beirut holding the Americans might compromise since their main purpose in seizing the Americans appeared to be the release of the two Lebanese Shiites. He said the two were related to the big and religiously important Mussavi family of Lebanon.

All of the other convicted terrorists are Shiites from Iraq except for one Lebanese Christian. They were convicted for their roles in a spate of bombings in Kuwait in December 1983, the worst of which occurred at the U.S. Embassy there.

John Weir said he had suggested the idea of asking Kuwait to release the two Mussavi relatives "at various meetings" in recent months with administration officials, including Ambassador Robert B. Oakley, head of the State Department's office for counterterrorism, national security affairs adviser Robert C. McFarlane and his aide in charge of day-to-day handling of the hostage issue, Lt. Col. Oliver L. North.

However, Weir said his father's Shiite captors had not included such a specific proposal in the message delivered to the Reagan administration upon his return. "But the one thing they did tell my dad is that they're flexible," he added.

Sen. Paul Simon (D-Ill.), who has been prodding the Reagan administration on behalf of the hostages' families, said Friday he thought the suggested compromise was "a possibility" that should be pursued.

"It seems to me it is a point at least worth exploring," he said.

John Weir said administration officials had been unwilling to acknowledge to the hostages' families that they were holding any kind of discussions with the Kuwaiti government over the possible release of even some of the 17 terrorists.

The administration has repeatedly said it will not compromise with terrorists or pressure other governments to make concessions. This stand was reiterated Friday by Vice President Bush in a meeting with the families of the six remaining American hostages.

"We're willing to meet with any responsible official to secure their release, but we cannot make concessions. None were made in the case of Dr. Benjamin Weir or in the TWA hijacking," Bush said, referring to the episode last June when Shiite terrorists seized a TWA airliner and held 39 American passengers in Beirut for 17 days.

NBC News reported last night that U.N. Ambassador Vernon Walters made a secret trip to Syria recently to ask President Hafez Assad for help in releasing the American captives in Lebanon.

Although there were hopes that Walters would gain release of all the Americans through his four-hour meeting with Assad, only Weir was subsequently released, NBC reported.