The performance of US military forces in Grenada was not without serious deficiencies and mistakes, according to a report released yesterday by the bipartisan congressional Military Reform Caucus.
In a stinging review of invasion planning, elite-force performance, helicopter survivability, and overall showing of both Army and Marine Corps units, this critique raises serious questions for the armed services and lays out lessons that are particularly relevant for any future United States actions in the region.
The Grenada operation has generally been viewed as a textbook conventional attack that ultimately fulfilled its missions of rescuing American medical students and stabilizing the political situation in the small Caribbean nation.
But this new review by military reform advocates points up just how difficult and costly ''unconventional'' warfare can be. And with every service demanding - and in this instance receiving - a piece of the action, it also illustrates the debate over service roles and missions.
The Military Reform Caucus is a group of 38 Republicans and 37 Democrats on Capitol Hill, chaired by Rep. Jim Courter (R) of New Jersey. This week's report was researched and written by William Lind, a congressional defense aide associated with Sen. Gary Hart (D) of Colorado and one of the leading scholars and proponents of military reform.
His principal findings:
* Even though US forces vastly outnumbered Cuban and Grenadan troops, deficiencies in planning allowed the latter ''to form and maintain a fairly effective defense.''
Mr. Lind found that early invasion plans called for using Navy and Marine Corps units only. Instead, he says, the Joint Chiefs of Staff (JCS) intervened so that the Army and Air Force were involved as well.
This resulted in some communication and coordination problems.
''In what seems to have become the standard JCS approach to military operations, one that turns them into a pie-dividing contest among all the services, we ended up with a plan that allowed the enemy to put on a reasonably good show,'' Lind writes.
* While the Army Rangers did very well in rescuing the American students, the Navy's elite commando group (the SEALs) failed in three of its four missions. The Army's antiterrorist unit - formerly known as the Delta Force; the name is now classified - failed to capture the Richmond Hill prison on Grenada.
* The Army's 82nd Airborne unit moved slowly in a classic frontal assault of vastly outnumbered Cuban troops rather than use infiltration and maneuver tactics. Lind thinks the Cubans could have been overcome in less than the three days it took.
* By contrast, the Marine units ''did not attempt to follow a rigid plan, but rather adapted swiftly to circumstances as they changed.''
* Of about 100 US helicopters used in the Grenada assault, nine were destroyed and several others damaged. ''A loss rate of 9 percent in three days against an opponent with no antiaircraft missiles, only guns . . . is not easy to pass over,'' Lind warns. ''What does it suggest our helicopter losses would be, for example, in a war in Europe?''
''Problems not corrected now will almost certainly arise again in future operations, with potentially high costs to national interests and casualties,'' says Lind. ''By learning as much as we can from the combat on Grenada, we may be able to save lives in the future and also improve our chances for victory.''
Representative Courter, who released the report, is a member of the House Armed Services Committee and (like most committee members) generally supportive of Pentagon programs and budgets.
But he says a closed-door Pentagon briefing on Grenada in January left him feeling ''that we had received one side of the story.''
Lind's findings, he told reporters, ''lead to some potentially disturbing conclusions.''
Mr. Courter this week also asked Armed Services Committee chairman, Rep. Melvin Price (D) of Illinois, to conduct an investigation of the Grenada invasion, focusing on the issues raised in Lind's report to the Military Reform Caucus.
In all, 18 US servicemen were killed in Grenada and 116 were wounded in an operation that cost $75.5 million and that the Defense Department and Reagan administration views as a success.
It was reported last week that the Army awarded 8,612 medals for performance in the operation.
These included achievement medals to about 50 people based at the Pentagon.