The Department of Justice, which has spearheaded the drive to test federal employes for drug use, is bracing to be sued by its own lawyers, who claim the proposed random testing is unconstitutional.

More than 100 Justice Department lawyers attended a meeting last week at which Arthur B. Spitzer, legal director of the local chapter of the American Civil Liberties Union, and former Maryland attorney general Stephen Sachs, who has agreed to represent the department lawyers for free, briefed the lawyers about the constitutionality of drug testing and the prospect of a legal challenge.

Meanwhile, Justice officials called off a plan to have large-scale briefings about the testing plan in favor of smaller meetings that Justice Department spokesman Patrick S. Korten said would be "less likely to be forums for some kind of grandstanding" by lawyers upset at the prospect of being tested.

Some department lawyers received a memo Oct. 28 informing them that their attendance was mandatory at a briefing on the testing program by Deputy Attorney General Arnold I. Burns. A terse memo issued the next day announced that the briefing "has been canceled until further notice."

Korten said the Justice plan, which officials hope to unveil by mid-December, is likely to be random testing of "litigators, especially those with access to grand jury material, people who have authority of one sort or another to make settlements involving large amounts of money, and those with security clearances," as well as presidential appointees.

"We're not proposing to test every lawyer," he said.

Korten said that Burns and Associate Attorney General Stephen S. Trott have been holding the smaller briefings with lawyers in the various Justice Department divisions, beginning last week.

"Although people have some concerns and worries, they seem to us to be generally supportive of the idea or at least not opposed," Korten said. He acknowledged, however, that the plan was "not as warmly received" at a meeting this week with civil rights division lawyers.

"People feel it's an insult," said one Justice Department lawyer, who asked not to be named. "Drug abuse is far from rampant around here, despite whatever image we might have these days," the lawyer said, referring to the recent disclosures of past marijuana use by Supreme Court nominee Douglas H. Ginsburg, a former assistant attorney general.

"We're not insulting anybody," Korten responded. "What we're trying to do is to ensure that no one in a sensitive position in a department charged with enforcing the nation's drug laws is himself or herself using drugs."

Sachs, now a partner at Wilmer, Cutler & Pickering here, issued an opinion as state attorney general last year finding that indiscriminate urine testing of Maryland state workers would violate the 4th Amendment prohibition on "unreasonable searches and seizures."

"A war on drugs is a good idea, but not if its first casualty is the Bill of Rights," he said.

Sachs said in an interview that the same conclusions would apply to Justice Department lawyers. "It doesn't follow that because somebody has access to grand jury information their privacy interest in private urination and keeping the contents free from examination" may be infringed, he said. He said the testing might be constitutional if there is "individualized suspicion" and a reasonable basis for believing that a lawyer is impaired.

The Transportation Department in September became the first civilian department to begin random testing to detect the presence of traces of marijuana, cocaine, opiate, PCP or amphetamines in the urine of its workers. The testing implemented for the first time President Reagan's year-old executive order to maintain a drug-free workplace.

U.S. District Court Judge Gerhard A. Gesell later dismissed a suit by the American Federation of Government Employees that attacked the plan as an unconstitutional search. Gesell said the testing program is reasonable, discreet and justified.

Asked how the Justice Department feels about the prospect of being sued by its own lawyers, Korten said such a challenge has been expected since the executive order was issued.

"It's a free country," he said.