Justice Department prosecutors around the country will begin investigations and "we contemplate some prosecutions" of 132 young men who have failed to register with the Selective Service, a department spokesman said yesterday.

A Selective Service official said that about 400,000 men have failed to register since President Carter reinstituted the program last year after the Soviet invasion of Afghanistan. The first referrals included those who actively defied the law, failed to respond to recent warning letters, or were turned in by complaining citizens, the official said.

Opponents of the draft vowed to fight the federal government's renewed enforcement activities. A leader of the Libertarian Party, whose presidential candidate, Ed Clark, got more than a million votes last fall, said many of the young men in the first referral were its members or officials.

Barry Lynn, leader of the Coalition Against Registration and the Draft, said the move proves that President Reagan "was misleading the American people when he promised during the campaign that this [registration] was something morally reprehensible."

While he was running against Carter, Reagan called the registration effort "an ill-considered one that should be rejected.Advanced registration will do little to enhance our military preparedness."

Since becoming president, however, some of Reagan's military advisers have questioned the adequacy of the all-volunteer armed forces, and have privately discussed a return to the draft.

Secretary of Defense Caspar W. Weinberger said in an interview with The Washington Post yesterday that "any time the law is violated you have serious problems if you don't attempt to secure enforcement of the law."

However, Weinberger, a lawyer, seemed to distance himself from the idea of rushing into prosecution.

"There are a number of ways to secure enforcement of the law, and prosecution is one of the ways," he said. "It's usually one of the last ways. There are a lot of things you can do short of that. I'm not taking any position on whether or not we should start prosecutions right now.

"It's now a major problem in size at the moment. A single bank robbery is not a major problem, either, statistically. I don't think you can ignore major violations of the law."

President Nixon ended the draft in 1973. Lynn said yesterday that Selective Service figures showed that during the Vietnam war era from 1964 to 1973, more than 200,000 referrals were sent to the Justice Department. Most involved young men who refused to report for induction into the Army, though there were some prosecutions of men who failed to register.

Of the referrals, more than 100,000 were declined because of procedural defects, Lynn said, while 82,000 men chose to be inducted rather than face prosecution. More than 25,000 young men were indicted, and 10,000 eventually went to trial. About 8.750 were convicted and about half of those served prison sentences.

When Carter began registration again last summer, men born in 1960 and 1961 were required to sign up at local post offices. This past January, those born in 1962 were required to register. Since then, men born in 1963 were expected to register within 30 days before or after their 18th birthday.

While 97 per cent of the first group and 87 per cent of the second registered on time, only about 70 per cent of this year's group of men turning 18 have registered so far, a Selective Service official said.