A national trial lawyers group, arguing against a proposal to restrict malpractice lawsuits, says that the reason there are so many medical suits is that there is so much medical negligence. "There is a medical malpractice problem; it is too much medical malpractice," concludes a 12-page report issued in response to recent suggestions by the American Medical Assn. for various limits on lawsuits. The report, by the Assn. of Trial Lawyers of America, comes three weeks after the American Medical Assn. recommended legislation to do away with punitive damage awards in malpractice cases.