Maryland obstetricians, hit hard by rising malpractice insurance rates, claim a plan to base their insurance premiums on the number of babies they deliver will hurt both them and their patients.

The proposal, by Medical Mutual Liability Insurance Society, is part of an average 32 percent malpractice insurance rate increase being sought for Maryland doctors. Medical Mutual insures a majority of the state's doctors.

Howard Friedman, assistant vice president for Medical Mutual, said the new method is designed to reflect the obstetricians' exposure to claims.

"The obstetrician who performs 150 deliveries has a higher potential for claims than one who does 50," he said.

Friedman said the increase is necessary because Medical Mutual paid one-third more in claims last year than in 1985.

But many doctors disagree, saying the proposal will hurt them and their patients.

Dr. Jay Greenberg, a Hagerstown physician said the proposal is very frustrating. If the increase is approved, it would affect the price of having a baby and doctors would be penalized for being successful, he said.

"When I came here six years ago, it cost about $400 to have a baby," he said. "Now, it's around $1,200 to $1,500. With the number of babies delivered affecting insurance, the doctor pays more the harder he works."