Persons convicted before July 1972 of possession of marijuana may petition to have their records sealed, under a Massachusetts law signed by Gov. Francis W. Sargent November 28.

Dealers of marijuana and other drugs are not affected by the law.

The record sealing provisions which go into effect December 28 state that persons who have no drug violations on their records except possession of marijuana may complete the petition, which will automatically seal the individual's record.

The bill, sponsored by State Rep. George Sacco (D-Medford), was passed in conjunction with a sealing provision law passed earlier this year. That bill limited access to records of people who had committed crimes no longer punishable by law.

The marijuana provision was written in conjunction with the Controlled Substances Act, which went into effect July 1, 1972.

Once a person's record is sealed, the person will have no criminal record in public dealings. This will allow him to answer on employment and license applications, for example, that he has not been arrested or convicted for possession of marijuana.

However, the Department of Probation retains a card with the felon's name. Under this system, 61 law enforcement agencies in Massachusetts can obtain the names of persons with felony convictions, Marsha Semuels, a spokesman for the Committee for a Sane Drug Policy, said yesterday.

Semuels said the courts also keep records because second offenses of drug laws require different penalties from first offenses.