Hysterectomies have passed tonsillectomies to become the nation's most commonly performed major operation, and thousands are done unnecessarily and sometimes for profit, two leading medical professors told a House Commerce subcommittee yesterday.

Only a "tiny percentage" are unnecessary, an American Medical Association spokesman replied, at a hearing where some Democratic congressmen shouted that the AMA is indifferent to needless deaths caused by such operations.

No one disputed the fact that the number of hysterectomies - operations to remove the womb - rose by what Dr. Kenneth Ryan of Harvard University called "a staggering" 25 per cent between 1970 and 1975.

By latest federal figures, 1975 saw 725,000 hysterectomies - or 3.47 for every 100,000 women - compared with 685,000 tonsillectomies and 319, appendectomies, among common operations. Among all surgery, hysterectomies were outnumbered only by 1.700,000 "D&C" - dilations and currettages, mainly for abortion.

The Commerce oversight subcommittee headed by Rep. John E. Moss (D-Calif.) has been investigating unneeded surgery for two years. It is now considering whether the law should require a doctor to get another doctor's opinion before doing any operation paid for by federal funds.

Both Dr. Ryan, Harvard's obstetrics and gynecology chief, and Dr. John Morris, gynecology chief at Yale, said hysterectomies are performed far too often.

Both said they should be done only for clear medical need and that two frequent reasons for them - for contraception or to prevent any chance of a future womb cancer by removing the womb - are plainly "excessive treatment."

The hysterectomy rate is higher among patients of surgeons who collect individual fees than among patients of salaried surgeons in prepaid health plans, Ryan added. (The fee for the operation and pre- and post-operative care runs between $850 and $1,500 in the Washington area, one source said yesterday.)

"If we want to eliminate unwarranted surgery, we have to control rising malpractice insurance rates," Morris said. "Some California surgeons now pay $100 a day for malpractice insurance. That can't help but affect some surgeons' judgment when they're considering an operation."

Dr. James Sammons, executive vice president of the AMA, conceded at the start of his testimony that "there is not 100 per cent unanimity" among doctors on the extent of unnecessary surgery or on anything else, and he called such diversity a strength that keeps medicine "vital and creative."

But for himself and the AMA, he denied strenuously that more than a few doctors have "a pecuniary motive." He said that most of what critics call unnecessary surgery is a matter of disagreement in judgment among able, conscientious surgeons.

He defended hysterectomies for sterilization "where a woman has acute pregnophobia," where where she is acutely fearful of being pregnant and no other method will reassure her," or where she cannot tolerate other birth control methods.

He likewise defended hysterectomies merely to prevent any chance of future cancer if a woman's fear of cancer is so great it upsets her mentally or emotionally, and a psychiatric consultant agrees that the operation will help reassure here.

Sammons' refusal to concede that more than a few surgeons do unwarranted operations caused Rep. Toby Moffed (D-Conn.) to accuse the AMA of "callousness" to patients' suffering. Rep. Andrew Maguire (D-N.J.) said, "The American people know there are thing wrong. This committee knows it. And you fail to address yourself to that issue."

But Sammons said the medical profession has begun to crack down on doctors who "ought not to be in practice" because they are incompetent or unworthy. He said 30 states have adopted an AMA model law to tighten the disciplinary powers of state licensing boards, and "in 35 states disciplinary actions" by such boards increased from 277 in 1971 to 936 in 1976.