The position of the United States Marines in Lebanon today is a graphic illustration of exactly what military professionals most want to avoid: an essentially political job that has (at best) only tenuous public support and allows for almost no way to succeed militarily.
And as investigations into the October bombing of Marine headquarters in Beirut proceed, questions are also being raised about whether in fact the Marines are the best force to be in Lebanon.
''If you're going to send forces in and out as a show of force, then it ought to be the Marine Corps,'' one senior officer says. ''That was the original intent of the operation. But then they found themselves fixed there.
''It seems to me that the Marine Corps is singularly unequipped for defensive warfare,'' this combat veteran continues. ''The Marine Corps is primarily trained as an offensive force and just doesn't think defense. That's a problem. They just don't think in terms of defensive operations the way the Army does almost as a matter of course.''
The dangers of sending military units to carry out what is basically a diplomatic mission also underlies Pentagon and congressional investigations into responsibility for the terrorist attack that killed 241 men. In its report this week, the House Armed Services subcommittee on investigations criticized ''a policy that placed military units in a deployment where protection was inevitably inadequate.''
''Most witnesses insisted that the policy in the Middle East and the mission of the Marines has not changed,'' states a summary of the House report. ''But between objectives, policy, mission, and conditions - something has changed. The subcommittee urges in the strongest terms that the administration review the policy in Lebanon from the standpoint of how the Marine mission fits into that policy. . . .''
The Pentagon's own investigation into the Beirut bombing, headed by retired senior military officers, is expected to include a review of and recommendations for changes in the Marines' mission there. At the same time, the Joint Chiefs of Staff is expected to suggest ways to deploy the American forces in a safer manner.
The report, submitted to Defense Secretary Caspar W. Weinberger Tuesday, is critical of security measures at Marine headquarters near the Beirut airport. According to senior defense officials, the report includes recommendations for increased security measures, some of which have already been taken.
It is not known, however, whether Secretary Weinberger will take disciplinary action against the military officers responsible for the operations and safety of the Marines in Lebanon. The armed services are not known for taking such actions when military operations (like the attempt to rescue American hostages in Iran) fail without clear proof of dereliction of duty. But judging at least from the House report, Congress seems to feel that individual blame will have to be assessed in this case.
''It is easy to be wise after the fact,'' the summary of the House report states. But the commander of the Marine amphibious unit that suffered the heavy casualties ''made serious errors in judgment in failing to provide better protection for his troops,'' the lawmakers charge, and ''higher command elements failed to exercise sufficient oversight. . . .''
The congressional investigators cited Marine Corps Commandant Paul X. Kelley and other senior officials for testimony following the bombing that was ''often inaccurate, erroneous, and misleading.''
The House study also pointed to ''serious intelligence inadequacies'' that affected the Marine unit's ability to defend itself ''against the full spectrum of threat.'' Experts point to this failing as rooted in the traditional role of the Marines. Most Marine Corps training and combat involves amphibious assault rather than taking and holding fortified sites for extended periods.
''If you're going to send a unit in for defensive operations, the Marine Corps is probably a poor choice,'' says a senior officer.
Such critical analyses of US military forces in Lebanon come just as polls indicate declining public support for continued deployment. They also reflect increasing congressional criticism of the administration's position, even from Republican and conservative Democratic lawmakers with solid pro-defense credentials.
For some time, senior military officers have warned the administration that the Marines could not count themselves as neutral ''peacekeepers'' once naval gunfire was used to defend Marine positions against attack from Lebanese militias. While the ''rules of engagement'' for US forces there have remained the same during the past year, the use of those forces has steadily escalated in a way that reminds many observers of Vietnam.
Yet, some analysts see a difference in that today's situation - the questionable use of military force in a difficult diplomatic and political setting - has been noted and is the subject of much debate and criticism here.
''There's an awareness of the problem, and that's very encouraging,'' says a senior military officer.