In assuming direct responsibility for the loss of US Marine lives in the Oct. 23 terrorist attack in Lebanon, President Reagan no doubt acted as most Americans thought he should.
A blame-stops-here attitude in the Oval Office can be helpful. President Truman's unapologetic firing of Gen. Douglas MacArthur, Eisenhower's acknowledging the U-2 flight over Soviet territory, Kennedy after the Bay of Pigs fiasco - such assertions of presidential authority can help a president govern during turbulent times. Johnson's decision not to run for office in 1968 was, in a way, his belated acknowledgement that the public held him responsible for Vietnam, an admission that his complex nature made difficult. In a different context, Nixon's refusal to accept the consequences of Watergate cost him his office. And Carter either overdid the appearance of responsibility, as in making himself hostage to the hostage seizure in Iran, or underdid it, as in blaming Americans' dim view of him on a societal malaise.
In the public's eyes, the marines in Lebanon became Reagan's marines when he sent them there. Moreover, it would appear unjust to assign blame down the line, militarily, when the principal decision placing them in jeopardy was from the top and political.
This said, there are other aspects to the Lebanon tragedy which demand careful accounting and redress. The burden of presidential decisions is that they impact on many others, including in this instance young men's lives and military commanders' careers. Chains of command, once set in motion, later require review under their own systems of accountability.
It would be too bad if the entire range of issues raised by the incident were cut off. Officers higher up the chain would dip into the Lebanon area a half a day and leave. The marines were far less protected than personnel at the US Embassy and those helping train President Amin Gemayel's troops. Marines are trained for assault missions; other troops would have been better geared to hunkering down and holding territory. And so forth.
Mr. Reagan's actual statement put the blame in a narrower context of defense against ''state-supported terrorism.'' ''I do not believe, therefore,'' he said, ''that the local commanders on the ground, men who have already suffered quite enough, should be punished for not comprehending the nature of today's terrorist threat. If there is to be blame, it properly rests here in this office and with this President. And I accept responsibility for the bad as well as the good.''
Critics contend that the terrorist threat should have been anticipated and steps taken to defend against an attack. A commander's first duty is to protect his troops. Many within the military worry that the President has in effect short-circuited the military's own review process. As commander in chief, the President was not absolving the commanders of responsibility so much as of culpability, which implies a prosecutable offense. It is crucial to clear up questions of accountability and conduct when they occur. Gen. William Westmoreland's lingering libel suit against a TV network - over a charge that a conspiracy within the US military had hidden the actual strength of the communist forces in Vietnam before the 1968 Tet offensive - suggests the tenacity of misgivings about civilian policy and military decisions and the importance of setting accounts straight early.
In any event, Mr. Reagan has likely deflected some of the political heat from two reports - one by Congress and one by the Pentagon - that trace the stripe of blame up and down the chain of command the President heads.
But the President still supports a continued Marine presence in Lebanon. He has not pulled the units back to safer ground or offshore.
The burden to prove that a military presence can deliver a diplomatic solution remains the President's. Mr. Reagan's up-front approach might not enhance his basic theory or dissuade his critics, but it helps cut short the acrimony that could otherwise develop.