President Reagan told congressional leaders yesterday that he has laid down "a marker for the Syrians" by moving a heavily armed U.S. Marine task force to the waters just off Lebanon, but he added that he has no present plan to commit these troops to combat.

Reagan's statements were passed along to reporters and confirmed by administration officials following a two-hour, 40-minute White House foreign policy briefing, one hour of which was devoted to fast-moving developments in the Middle East.

There was no indication that the administration has decided whether, how or when to report this latest U.S. military deployment officially to Congress under the War Powers Act. A report under certain sections of the act would trigger a 60-to-90-day time limit in the absence of congressional authorization of the troop movement. One congressional source said lawmakers have been promised they will be consulted on this point before Congress reconvenes a week from today.

The task force of about 1,900 Marines, which was reported to be approaching the Mediterranean through the Suez Canal, was ordered to the area after two of the 1,200 Marines already on peace-keeping duty in Lebanon were killed last Monday as serious violence erupted in that strife-ridden country.

In an unsuccessful last-minute bid to allow more time for negotiations among warring groups within Lebanon, Reagan telephoned Israeli Prime Minister Menachem Begin shortly after noon Saturday to appeal for another postponement of the long-forecast redeployment of Israeli troops near Beirut, administration sources said.

The Israeli government replied several hours later through the State Department that the request had been "too late" and the repositioning was already under way, the sources added. Reagan indicated that he accepted this reply with understanding, telling a reporter in a brief photo session exchange yesterday that his plans in the Middle East had not been spoiled by the Israeli action and noting that Israel "had already delayed twice."

White House spokesman Larry Speakes quoted Reagan as telling the congressional leaders that "we are at a critical point in trying to establish peace in the area."

In yesterday's round of fighting, which took place as Israeli troops moved back to new positions for the longer haul, U.S. Marines near the Beirut airport reportedly fired small arms in self-defense when caught in a cross fire between Lebanese Army troops and Druze Moslem fighters. One Marine was hit in the left arm by shrapnel, treated and returned to duty.

House Majority Leader James C. Wright Jr. (D-Tex.) said the leaders were told in the briefing that the arriving task force was "to reinforce the mission of the Marines who are on shore, that they do not intend or expect to go ashore, that they are there primarily to demonstrate that we do not expect nor would we tolerate any attack on our U.S. forces there in Lebanon."

Some administration officials have blamed Syria for the latest outbreaks of fighting, maintaining that Syrian failure to withdraw its forces from Lebanon is an indirect cause of the strife and charging that Syria has encouraged Druze and Shia Moslem groups to challenge the Lebanese government.

Reagan's remark that the new U.S. force is "a marker for the Syrians" suggested that among its major missions are deterrence of Syrian involvement and/or military reaction in case of renewed challenge to U.S. peace-keeping forces or interests. The 1,900 Marines in the arriving task force are backed up by large-scale naval forces, including the aircraft carrier USS Dwight D. Eisenhower.

Yesterday Syrian tanks in Lebanon were strafed by Israeli fighters as they sought to occupy positions being left by Israel, according to reports from the area. This was described as the first direct military clash between Syrian and Israeli forces for many months.

The engagement of U.S. military forces in a major clash with Syria would add a new dimension to American involvement in the Middle East and have serious regional as well as international repercussions. Syria is a radical Arab state on the front line of Israel, and it is advised, equipped and backed by the Soviet Union.

State Department officials described the dispatch of the new U.S. task force to the waters off Lebanon as "a general precautionary move" to provide American muscle and flexibility in case the Marines already on shore are challenged seriously. The officials said France has also brought in an aircraft carrier and other offshore units to back up the onshore French troops of the multinational peace-keeping force.

There had been suggestions that the international troops of the peace-keeping force might expand their forces and areas of activity in the wake of the Israeli repositioning.

Speakes said in a briefing on the leadership meeting, however, that there are "no plans to change the mission" of the U.S. troops of the peace-keeping force. Members of the congressional leadership said they were promised that lawmakers would be consulted if additional U.S. troops were to be furnished to this force.

House Speaker Thomas P. O'Neill Jr. (D-Mass.) said there is "no consensus . . .whatsoever" that the Marines on duty in Lebanon should be brought home under the current circumstances.

O'Neill said that in his opinion "the president made a mistake" in failing to report the original dispatch of the Marines to Lebanon last fall under binding provisions of the War Powers Act. The speaker said he believes the House would have acted to authorize this use of U.S. military power if it had been presented under the War Powers Act last fall, and he indicated the House probably would vote positively on the onshore U.S. Marine presence if presented with the issue now.