If you need surgery, the bigger and busier the hospital and the more operations of the type you're undergoing are done there, the better your chance of emerging well and alive.

This is the conclusion that can be drawn from a new study of infection rates after surgery.

This, plus a landmark study a year and a half ago that showed that hospitals that do the least surgery have the highest death rates, are "a clear lesson" for patients, one of the new study's main authors, Dr. Richard Wenzel of the University of Virginia, said yesterday.

Anyone facing surgery, said Wenzel, should ask the surgeon how many similar operations are done every year at the intended hospital and how many the surgeon does.

"I think in a few years most sophisticated patients will be asking such questions," he said. "If a surgeon or hospital did just a handful of such operations, I'd look for a surgeon that did 50 at a busy hospital."

There are many exceptions to these general rules, he emphasized. There are small, less busy hospitals that do very well. But in the absence of other information, Wenzel said, "I think such studies tell the patient where he is likely to have the best chance."

Hospital infections are one of medicine's most stubborn problems. Some develop from the patient's bacteria, but most come from drug-resistant bacteria colonies that have become established in the hospital.

There are an estimated 300,000 post-operative wound infections yearly in American hospitals. No more than 1 percent are fatal, but this means 3,000 deaths yearly. Many others are serious.

Wenzel and Drs. Bruce Farber and Donald Kaiser at the University of Virginia Medical Center in Charlottesville studied infection rates in several kinds of surgery at 22 unidentified hospitals, most in Virginia but including two in other parts of the Washington area. All were community, not university or government, hospitals.

Infections occurred in 5 percent of cesarean sections and appendectomies and 7 percent of hysterectomies. They occurred in 10 percent of colon operations (the colon is filled with bacteria), but only 1 to 2 percent of back and hernia operations and gall bladder removals.

Although there are exceptions, there were often three to four times as many infections at a hospital that did a particular operation perhaps less than 50 times a year compared with a hospital that did 200 or more.

The most probable reasons for the best records, Wenzel said, are skill and experience of the operating surgeon and the hospital team and better procedures for infection control.

The study appears in today's New England Journal of Medicine. In late 1979 a Stanford University University of California group reported there that hospitals that did heart, blood vessel or prostate operations at least 200 times yearly had death rates 25 to 41 percent lower than hospitals that did fewer.

The California group said these figures support the idea of "regionalizing" some operations, performing them only at skilled regional centers rather than every hospital.