WASHINGTON (AP) _ A judge heard final arguments Friday on whether marijuana has a medical use, with proponents contending that the drug can help people suffering from a variety of diseases and the government maintaining that the drug's safety has not been proven.

Administrative Law Judge Francis L. Young did not specify when he would make his recommendations on the issue to the head of the Drug Enforcement Administration, but lawyers for both sides said they expected Young's ruling by late summer or early fall.

At issue in the 16-year-old case is whether marijuana should be reclassified from a Schedule I drug - where it, like heroin and LSD, cannot be produced by pharmaceutical companies and has no accepted medical use - to a Schedule II drug that can be marketed for medical uses.

The hearings before Young began last November in New Orleans, continued in San Francisco in December and moved to Washington in January. In that time, legalization advocates, among them the National Organization for the Reform of Marijuana Laws and the Alliance for Cannabis Therapeutics, presented dozens of witnesses who said marijuana could help cancer patients suffering from nausea from chemotherapy treatments, glaucoma sufferers and people with multiple sclerosis and a host of other neurological diseases.

Attorney Kevin Zeese, representing NORML, told the judge that thousands of people were tested after using marijuana for medical reasons in federally approved state experiments, and ''the lack of side effects was astounding. The most common side effect was fatigue and dry mouth, which are not significant compared to the side effects of other drugs commonly prescribed to these people.''

Attorney Frank B. Stilwell III, representing the Alliance for Cannabis Therapeutics, argued that ''society at large accepts marijuana as a medicine'' and said the DEA ''is so caught up in the drug war, it is afraid to say that marijuana has medical uses.''

Charlotte Mapes, representing the DEA, countered that marijuana is a complex drug whose effects are not known completely and that further testing is needed. She also said that groups like the American Medical Association had not endorsed the use of marijuana for medical purposes.

''Aren't there politics involved in the AMA's position?'' the judge asked Ms. Mapes. She said there were.

The judge at another point asked Ms. Mapes whether she agreed with arguments by the legalization advocates that the federal government's standards on drug legalization were slanted toward synthetically produced drugs.

''They argue that we have a situation where monied pharmaceutical companies are willing and able to send great sums of money to win approval for drugs,'' Young said. ''The petitioners argue that the federal standards are not slanted toward natural drugs.''

Ms. Mapes responded that the Food and Drug Administration ''is constructed toward the needs of pharmaceutical companies,'' adding, though, that ''the federal standards for drug approval are also accepted by the medical community.''

The case dates back to 1972, when NORML petitioned the DEA to remove marijuana from its drug schedules, in effect, to decriminalize possession of the drug.

The DEA took no action in the case until 1979 when it announced that it would continue to classify marijuana as unfit for medical use. NORML, by that time joined by the Alliance for Cannabis Therapeutics, appealed to the U.S. Court of Appeals in Washington. And the court ordered the DEA to reconsider its action and to conduct hearings on the issue.

Also arguing against legalizing marijuana for medical use at Friday's hearing was Karl Burnstein, president of the National Federation of Parents for Drug-Free Youth, based in Silver Spring, Md.

Burnstein said his group was concerned that ''if marijuana would be rescheduled, what kind of message would that be sending to this nation? Our citizens are not familiar'' with the details of federal laws, he said, adding that he feared the nation's youth would say that ''if marijuana is good for all these (medical) things, why isn't it good for me?''