CRISIS IN THE BALKANS : The Post-Traumatic Stress Syndrome of Post-Vietnam Policy : Military: Lurking in background of debate over U.S. involvement in Bosnia is the Southeast Asia quagmire. But officials downplay any similarities.

President Clinton’s new policy on Bosnia-Herzegovina has raised fears among some military experts that the United States may be embarking on a strategy of “gradual escalation” similar to one that led to the American defeat in Vietnam.

Top military leaders so far have publicly supported the President’s willingness to consider letting U.S. troops move embattled U.N. peacekeeping forces to safer positions. But in the background lurks a concern that the United States may be nearing a “slippery slope” into a far deeper conflict.

Critics contend that many of the elements are present for the United States to get bogged down in a Vietnam-style quagmire, with one side ratcheting up the fighting in hopes of ending the hostilities, only to set off a response in kind by the other.

The result in Vietnam was a protracted, full-scale war, the only one the United States ever lost, at the cost of 55,000 American lives overseas and violent political divisions at home.

Bosnia remains a long way from being “another Vietnam.” The United States, at its peak deployment, fielded more than half a million ground troops in Vietnam. It has no combat troops in Bosnia and has proposed using a limited force of a few thousand for only a temporary period of time.

In Vietnam, the United States was on its own, seeking to stop the forces of nationalism in a little-understood part of the world. In Bosnia, by contrast, the United States and its allies are acting under U.N. auspices, and their more limited goal is to keep rival ethnic groups from deadly conflict.

“We are participating in a narrowly defined way in an ongoing U.N. peacekeeping operation,” White House Press Secretary Mike McCurry said this week.

He added that Clinton would act only if he could establish “a very clear definition of purpose [and] an exit strategy.”

Nevertheless, at least on the surface, recent developments in Bosnia seem ominous:

* In response to hostage-taking by the Bosnian Serbs, the allies have already dispatched small units of commandos to bolster U.N. peacekeeping forces in Bosnia, and Clinton has deployed 2,000 Marines to the region to stand by in case of emergency.

* The Europeans are considering a plan to up the ante by creating a small rapid deployment force that could be rushed anywhere in Bosnia to aid peacekeeping units in trouble.

* And on Friday, Bosnian Serbs shot down a U.S. Air Force F-16 jet fighter--a move that could spark retaliation in the form of harsher air strikes by the North Atlantic Treaty Organization. The Bosnian Serbs returned some U.N. hostages Friday, but the situation remained tense.

Even the new allied plan to consolidate the peacekeepers by moving them back near the Bosnian capital of Sarajevo--an operation for which Clinton has said he may provide some U.S. troops--brings tremors to some experts. Well before the United States committed troops to Vietnam, the French used a similar tactic by grouping their troops in Dien Bien Phu, with disastrous results.

“If you liked Dien Bien Phu, you’ll love Sarajevo--this policy is nuts,” said Dan Goure, a former Pentagon strategist who is deputy director of political and military studies at the Center for Strategic and International Studies, a defense-monitoring group.

“We’re at the stage where [Defense Secretary] Bill Perry is going to write his McNamara mea culpa 30 years from now,” Goure said.

Robert S. McNamara, who was defense secretary in the Vietnam War, has just written a book saying U.S. policy was wrong in the debacle.

A senior military officer agrees that there is potential for the Bosnia policy souring: “There’s a real conviction here [in the Pentagon] that going in there and establishing roots in the Balkans is a bad idea and a loser,” he said. “In my view, it’s a powder keg.”

The American experience in Vietnam has become a classic example of how not to conduct a war.

When the United States formally entered the conflict in 1961, it sent only a few thousand military “advisers,” intending to keep them out of direct fighting.

But over the next several years, North Vietnamese retaliation drew the United States deeper and deeper. By 1969, when the war hit its peak, the United States had more than 500,000 combat troops in Vietnam, and American casualties were running into the thousands each week.

Administration officials say that, despite seeming similarities, the Bosnian situation is far different. And they argue that even under Clinton’s new policy, the United States still is a long way from becoming embroiled in another Vietnam.

Clinton has insisted that he will not send U.S. ground forces into combat in Bosnia. His Administration says it wants no part of a new French proposal to create a quick-reaction force. And the White House has vowed that U.S. troops will not serve as peacekeepers.

But critics point out that Clinton has already moved significantly from assertions he made earlier in his term, when he pledged that the United States would not send any ground troops to the region, no matter what the circumstances.

Even helping to evacuate U.N. peacekeeping forces--as Clinton has pledged he would do, if the allies ever decide to withdraw from Bosnia--runs a risk of high U.S. casualties.

The prospect of helping U.N. troops consolidate in the interim only heightens that danger.

And, as Friday’s shoot-down demonstrates, even U.S. fighter pilots are no longer as safe as they once were. Bosnian Serb forces now carry shoulder-fired surface-to-air missiles that can easily down a low-flying aircraft.

Moreover, some knowledgeable officers believe that for all the Administration’s assertions to the contrary, the White House appears to be leaning toward increasing military involvement in Bosnia and is vulnerable to appeals from longstanding U.S. allies.

“I think they’re heading in that direction, even though they may not be willing to admit it yet,” one officer said. “I’m not really sure that they’ve worked out exactly what they want to do.”

So far, at least, military officials appear unworried. Until the Administration has put U.S. troops on the ground, it still has not crossed the line into the area of tit-for-tat escalation, one well-placed officer noted. “There’s still time to back off.”

Moreover, military officers say that, while the Administration may end up erring initially by sending in too small a contingent, they are confident that, if the President decided to take the Bosnian Serbs more seriously, he would order up sufficient force to overwhelm them quickly.

“We’ve learned our lesson from Vietnam,” one key military planner said. “In the Gulf War, in Somalia and even in Haiti, we went in initially with large numbers of troops, planes, tanks and ships. And we’re not likely to repeat the mistakes of Vietnam any time soon.”