Montgomery County School Superintendent Charles M. Bernardo yesterday reprimanded and ordered the reinstatement of a high school teacher who was suspended early this month after suggesting that those of her students who smoke marijuana ought to determine if it had been contaminated by a toxic chemical.

Bernardo placed an official letter of reprimand in the file of the teacher, Andrea Brown, for"handling the marijuana contamination notice in an inappropriate manner" and permitting other inappropriate drug-related material" on a classroom bulletin board, according to school spokesman James E. Lashley.

The reinstatement order becomes effective today. Brown said yesterday she would return to her regularly scheduled English literature classes this morning.

"I've got a mixture of emotions" about the reinstatement and reprimand letter from Bernardo, she said. "If (the chemical) is hazardous, then people ought to be warned about it. That's what I was trying to do," she said.

Her attorney, Gary Howard Simpson, said he did not know what action, if any, he would take regarding the letter of reprimand now in his client's file.

Brown, 30 was suspended with pay on April 3 after leaving on her classroom desk mimeographed copies of the name, address, and phone number of a California laboratory that would test marijuana samples to see if they had been contaminated by Paraquat, a highly toxic chemical herbicide.

Simpson said last week that Brown made the copies after reading in The Washington Post of a report saying Mexican authorities had sprayed Paraquat on marijuanafields in an attempt to eradicate it in a drug control program partially funded by the U. S. State Department. The report by the Department of Health, Education and Welfare said irreversible lung damage could result from smoking marijuana.

In a letter to Simpson, Bernardo "commended" Brown for her "concern about the health problems that could result from students' using contaminated marijuana." Bernardo said he based his reprimand on what he said was her permitting "other inappropriate drug-related mateial to remain on her classroom bulletin board and for hanrial to remain on her classroom bulletin board and for hanate manner."

The "other inappropriate drug-related materials" were not specified, but Simpson said he believes they were material related to drugs and to a marijuana pipe that students had placed on a thin strip of wall. "It's the place where students can express themselves" rather than the official classroom bulletin board.

Simpson questioned Bernardo's assertions in his letter that Brown should have either counseled student's individually about marijuana use or suggested taking "an institutional approach by trained personnel.'

"If she had taken the individualapproach, it would have caused embarrassment to students, since she had no way of knowing who was smoking marijuana," he said. He called the institutional approach a "pipe dream. The school system itself has yet to solve the situation of students who smoke," he said.

Brown was suspended because officials believed she might have violated a school board policy prohibiting teachers from doing anything to "condone or encourage" drug abuse. Officials said the reinstatement came when Bernardo determined she had not violated that policy.