The battle over bringing back the draft was formally joined in Congress yesterday, the first full-dress debate on the subject since the Vietnam war.

The emotional exchanges in a crowded House Armed Services committee room signaled that lawmakers bent on restoring conscription, when there is no war, will come under heavy fire from libertarians.

"A severe infringement of individual liberties," said the American Civil Liberties Union, in testimony that also questioned whether the Pentagon needs any more men than it is already gotting through volunteers.

To draft young people under current conditions, contended ACLU attorney David Landau, "is constitutionally impermissible." A number of representatives and senators have introduced bills to require 18-year-olds to register for the draft, and some measures would restore actual conscription.

"The draft is nothing less than a form of involuntary servitude," said ACLU. "Conscription should be the last resort of a nation facing imminent threat."

The civil liberties pressure group also attacked the idea that young people should be forced to perform some other kind of government service if they did not go into the military. This, said Landau on behalf of ACLU, "would introduce into our country regimentation principally associated with totalitarian states."

The General Accounting Office has suggested that the government could compile a list of draft-age Americans by going through data held by federal and local governments, such as drivers' licenses and voter registrations. Compiling such a list, complained the ACLU, "poses a massive threat to individual privacy" that the 1974 Privacy Act was designed to prevent.

Opponents came to the hearing loaded with ammunition they had obtained from a recent Pentagon report, which said the all-volunteer force is doing well.

But Rep. Robin L. Beard (R.-Tenn.), a reserve Marine major, declared that the Pentagon did not know what it was talking about when it wrote that rosy assessment. He contended that the all-volunteer force is a failure, and that the draft is desperately needed to obtain critical skills ranging from those of tank drivers to doctors.

"There is an overt cover-up by the Department of Defense, and especially by the Department of the Army," on how had off the services would really be if war broke out, Beard said.

The Army alone, he said, estimates that it would need 600,000 draftees after the first 60 days of a European war. But the Selective Service is planning on having 60 days to draft the first 100,000 men.

Also. Beard complained to the witnesses objecting to the draft on libertarian grounds, the burden of military service is not being shared equitably today. By 1980, said Beard, 45 percent of the Army's junior enlisted people will be black and 65 percent of those with six or more years of service will be black.

"We're getting the kid who has no place else to go," said Beard in maintaining that the all-volunteer force has proved to be unfair.

Rep. Lucien N. Nedzi (D-Mich.) agreed. "Infantry and armor work is dirty work," Nedzi said. "Nobody wants it. It's unfair to place that burden on minorities. It's exactly what was predicted, and it's exactly what has happened."

Rep. Marjorie S. Holt (R-Md.) told the conscription critics at the witness table that the Soviets are "weaving a web around the Persian Gulf." The United States must "show them that we have the will to keep our civil liberties."

"Do you subscribe to the theory that being strong deters aggression?" subcommittee Chairman Richard White (D-Tex.) asked Barry W. Lynn, counsel for the United Church of Christ.

"We have enough, if not too much," Lynn answered. He said the Defense Department should provide "more data" on whether it was realistic to expect any land war in Europe to last more than six months, and thus require reinforcements, before nuclear weapons were fired.

The draft expired in 1973. President Carter is asking Congress for extra money for the Selective Service this year. Acting Selective Service Director Robert E. Shuck added some comic relief to yesterday's hearing by declaring that he personally opposes registering and drafting women until men learn how to have babies.