The Maryland Motor Vehicle Administration is going to make it tougher for teen-agers under the state's legal drinking age to obtain phony driver's permits.

Since Maryland's legal drinking age was raised from 18 to 21 July 1, some underage teen-agers -- in an effort to buy liquor illegally -- have been renting or borrowing the birth certificates of older people and using those documents to obtain fraudulent duplicates of driver's licenses, MVA administrator William T. S. Bricker said yesterday.

Spurred by an investigation of a Howard County restaurant which resulted in the arrest of five juveniles, Bricker's agency now will take two photographs of anyone under 24 who applies for a duplicate license. One photo will go on the license, the other will be kept on file. The agency also will require three or more forms of identification at the time of application and will begin issuing a 20-day temporary duplicate permit to give officials time to check the authenticity of the documents.

Teen-agers frequently use the birth certificate of a close friend or older brother or sister to obtain duplicate permits, Bricker said. Sometimes one document is passed among several applicants. Officials picked 24 as a cutoff age because they felt 21-to-24-year-olds were most likely to lend their birth certificates.

"The youngsters use these illegal duplicates to buy liquor or to get into clubs and other places that serve alcohol to their customers," Bricker said. "Although most establishments have an employe who checks the IDs . . . it is difficult for them to tell whether the driver's permit is legitimate."

In a recent computer check of the state's 476,000 drivers between the ages of 18 and 24, the agency found that 1300 duplicate permits were issued between May 1 and July 31.

"We have no way of knowing exactly how many of those were fraudulent," Bricker said. He noted that the penalty for obtaining a phony driver's permit in the state is one year in jail and a $1,000 fine.

During the Howard County raid, police discovered that one of the youngsters was only 15. Another appeared to be about 12, but the permit said she was 20. One permit had been duplicated five times.

Jim Corrington, general manager of the Sea Galley in Columbia where the bogus permits were uncovered, said he called police to his establishment two weeks ago after it appeared that an increasing number of his customers were "very young."

"I had to decide whether I was going to call the police and maybe lose a lot of business or keep serving liquor to these kids and maybe lose my liquor license."

The day after police detectives spent three hours checking IDs in his restaurant, business was slow, Corrington said. "But on the following weekend the crowds picked up again. Our customers seem to be much older now."