Investigations of the bombing of Marine headquarters in Beirut now shift from establishing responsibility to looking for ways to prevent a recurrence. If the recent historical pattern is followed, formal disciplinary action against military officers involved is not likely to occur. It didn't following the Mayaguez or Iran rescue missions, which similarly resulted in loss of American lives. And court martial proceedings against the captain of the captured United States intelligence ship Pueblo were dropped.
But there is no doubt now that the careers of some senior officers will be affected by the tragedy of October 23, which left 241 dead and seriously called into question the presence of US military forces in Lebanon. The results of both congressional and Pentagon investigations confirm this. More broadly, the armed services are sure to feel the impact of the fundamental reexamination now taking place of the chain of command leading from Pentagon civilians to commanders in the field.
Officers throughout the services are feeling defensive as well as protective of their fellow officers directly involved in the Beirut bombing. Yet there also is a sense among many that responsibility must be fixed in this instance and authority more clearly established in the future.
''The tradition that a commander is responsible for all that his forces do or fail to do is a very harsh tradition, and it's sometimes very unfair,'' says one senior officer. ''But I think for the good of the armed forces, it has to be enforced.''
At the same time, this combat veteran noted that in recent years, ''responsibility has become so diffused that no one is responsible for anything. . . . The problem with Vietnam was that everybody and nobody was responsible.
''One of the things that's happened to our armed forces over the years, because of modern communications, has been an arrogation of authority by Washington and higher headquarters, leaving the responsibility in the hands of the commander in the field,'' says this officer of many years' experience. ''And because of this, it's very difficult to fix blame when something happens. I think that's probably the lesson to be drawn from this.''
It appears now that at every link in the military chain there was insufficient recognition of the fact that the threat to the marines in Lebanon was changing in ways that reflected - and should have changed - their role there.
From neutral ''peacekeepers'' and ''local heroes,'' they became partisans and targets. Yet they failed to protect themselves from what in that region had become the most frequent form of terrorist attack. They were caught between what they assumed should be a high-visibility mission of ''presence'' and the increasing need to beef up security.
And there was a certain amount of pride involved as well. The Marine commander said later he did not want to give the impression ''that we were cowering.'' He did not ask for more protection, nor did his superiors who frequently visited Beirut order or even suggest the simple protective steps that could have prevented the costly truck bombing.
This contrasted with the much heavier security surrounding the US and British embassies, the Lebanese President, and the US Army unit there to train the Lebanese Army. ''Only the MAU (Marine amphibious unit) thought that it had to keep a high profile,'' the House investigations subcommittee reported.
And even after the bombing, there apparently was some resistance to fortifying Marine positions sufficiently. Several weeks after the bombing, the NATO commander, Gen. Bernard Rogers, found it necessary to order such measures.
As commander in chief and secretary of defense, President Reagan and Caspar Weinberger acknowledge, as part of their constitutional duties, bearing ultimate responsibility for the deployment and safety of US troops abroad. At the same time, however, their defense policy has clearly included the increased devolution of military authority in the field to the armed services. This policy is at least indirectly called into question by the Beirut bombing.
Both the Pentagon and the White House are carefully studying the congressional report as well as one by retired senior military officers expected to be made public this week. Both reports are critical of the decision - and in some cases, the lack of decision - by officers in the complex chain reaching from Beirut to Washington.
The House report is particularly critical of the Marine Corps commandant, Gen. Paul X. Kelley, who is charged with having given testimony shortly after the bombing that proved to be ''erroneous, misleading, and often contradictory.'' The Marine Corps says its senior officer was providing the best information available at the time.
But this illustrates two important points. First, the commandant's prime interest in asserting that the bombing could not have been foreseen or prevented was to bolster Marine Corps morale in the wake of the tragedy.
Second, General Kelley, as a member of the Joint Chiefs of Staff, is not part of the military chain of command and thus would not have been in the best position to keep abreast of combat (or in this case, near-combat) actions by the service he oversees.
House-passed legislation now under Senate consideration would place members of the Joint Chiefs in the chain of command.
The on-scene Marine Corps commander is faulted in the House report not for neglect or dereliction of duty, but for ''misjudgment with the most serious consequences.'' At the same time, the ''absence of independent oversight and evaluation'' by higher-level commanders is cited, along with civilian leadership that ''paid insufficient attention to the difficulties of the mission it assigned.''
The congressional and Defense Department probes illustrate the armed services' difficulty in assuming noncombat goals designed to bolster foreign policy. ''It would be better if the generals and colonels weren't expected to be diplomats,'' House investigators concluded.
The results of the investigations are likely to be felt in two areas: within military operations and in how Congress acts regarding the administration's Mideast policy.