President Reagan yesterday asked for a full report on why a team of U.S. soldiers carried M16 rifles in a potential combat zone in El Salvador in apparent violation of the administration's guidelines, but he said the soldiers' actions were "understandable."

The administration responded to congressional concern about U.S. advisers last year by ordering the troops not to carry combat weapons or to travel except where government forces have established control.

"The only thing I can assume is that they the rifles were for personal protection and I think that's understandable. But I'm asking for a full report and we'll have one from the Defense Department," Reagan said in a brief exchange with reporters as he left the White House for a weekend at Camp David.

"The policy is we do not engage in combat. Nor were these gentlemen, as far as indicated, doing that at all," he said.

A camera crew from Cable News Network videotaped three U.S. advisers dressed in civilian clothes carrying M16 rifles. It was the first time reporters had seen any of the 50 U.S. advisers in El Salvador carrying combat weapons in an area where leftist guerrillas are active.

Larry Speakes, deputy White House press secretary, said the men videotaped near the village of El Delirio, about 12 miles from the provincial capital of San Miguel in eastern El Salvador, were members of a special team on a three-day assignment in El Salvador.

He said the team consists of a warrant officer and four enlisted men and was helping with a bridge-building project. Speakes said he did not know why they were wearing civilian clothes.

They were not part of the main U.S. training mission in El Salvador, Speakes said, and were due to return to the capital, San Salvador, yesterday to be questioned by the commander of the training mission.

Speakes said the area where they were working is regarded as government-controlled, but that it "was subject to outbreaks of violence and the people there were subject to substantial risk."

Last May, the State Department said, "Personnel will be stationed in San Salvador or in carefully selected regional garrisons and special precautions will be taken to provide security for them. They will not go on patrol or combat missions with Salvadoran forces nor will they otherwise be placed in situations where combat is likely."

The Pentagon issued a statement that "some of the trainers were carrying M16 rifles," which was unauthorized, but that Americans "were not and have not been involved in combat activities."

U.S. military men in El Salvador are authorized to carry only sidearms, the Pentagon said. They have been issued M16s, which they are required to keep in their quarters, to defend themselves in case of an attack.

Sen. Paul E. Tsongas (D-Mass.) watched the CNN videotape yesterday and questioned whether the U.S. bridge-building team's actions triggered the provision of the War Powers Resolution of 1973 that requires the president to report to Congress in writing within 48 hours of the introduction of U.S. armed forces into "hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances."

Tsongas said he would ask for a report on U.S. military personnel activities in El Salvador when Congress reconvenes Feb. 22.

Reagan also was asked whether U.S. Ambassador Deane R. Hinton was speaking for the president when he criticized "serious excesses" by the Salvadoran government. "I just heard all of you on the news not too long ago, not very much time was given to it, but there was a mention that the guerrillas had attacked a village up on the Honduran border and it was reported that 100 people were killed," Reagan replied.

"I consider that a violation of human rights. We know that there have been problems from both the left and the right. That's why we're supporting the Jose Napoleon Duarte government, which is between both of these factions, both of which have been somewhat extreme," the president said over the noise of his helicopter engine.

Reagan's answer apparently referred to the Salvadoran government's claim that guerrillas killed 150 to 200 civilians in an attack on a military garrison Jan. 30 and it did not respond to the ambassador's point, which was that Duarte government forces had committed serious violations of human rights.

In another development, the Justice Department asked U.S. District Court Judge Joyce Hens Green to dismiss a suit by 29 House members that seeks to end all U.S. aid to El Salvador. A Justice attorney said the House members want the court to take away the president's right to conduct foreign policy. CAPTION: Picture 1, Reagan: "The only thing I can assume is that they [the rifles] were for personal protection and I think that;s understandable." By Harry Naltchayan --The Washington Post; Picture 2, This photo taken from a Cable News Network monitor shows a man carrying a briefcase in one hand and a weapon in the other. AP; Picture 3, A U.S. military advisor is shown taking a .45 caliber pistol, an unauthorized weapon from his belt in this scene from television. AP