During the past 13 monts at least 20 patients with heart disease have been given replacement aortic valves that have turned out to be contaminated with bacteria, according to the federal Center for Disease Control.

The firm that prepares aortic valves of pigs for use in humans, Hancock Laboratories Inc., of Anaheim, Calif., has voluntarily recalled all the valves processed between October, 1975, and July, 1976, to be exchanged for new valves.

Officials of Hancock, the CDC and the federal Food and Drug Administration, all stressed that there have not been any deaths associated with the contaminated valves and that the 20 are a minuscule percentage of the more than 10,000 similar valves implanted during the same time period.

Two patients, including a 55-year-old man who had one of the valves implanted at the Washington Hospital Center last December, have become ill with symptoms normally associated with mycobacterium chelonei, the "bug" found on test "coupon" packaged with the valves.

The "coupon" is a small piece of the material that forms the valve, and is packaged with the valve in order to give the hospital implanting the device a way to test the sterility of the valve.

The valve itself cannot be tested because it must be implanted as soon as the package is open to prevent the valve from being contaminated in the hospital. In fact, the problem of the coupon being contaminated is so common that the FDA recommended to hancock that it stop including the coupon because the precaution was unnecessarily scaring physicians and patients into thinking the valve was contaminated.

Dr. Mack Hooten, the CDC official monitoring the problem, said that "as far as the risk to patients, it's up in the air. We're at a loss here as to what way things should go." However, he said, "We're taking it seriously."

Dr. Manuel Tascon, medical director for Hancock laboratories, has suggested that any contamination that may have existed most likely originated in the hospitals where the surgery was performed.

Additionally, Tascon said in a telephone interview Saturday, that "There have not been patient complications to our knowledge, except maybe, maybe, one . . . The patients are alive due to the valve itself," said Tascon, who expressed great concern that patients would be unduely alarmed by any publicity about the problem.

In the case of a woman who received the valve in a St. Louis, Mo., hospital, bacterium, similar to the bacterium which causes tuberculosis, was found in her body as well as on the "coupon" packaged with the valve.

The Washington case, however, is a bit more circumstantial. The bacterium was found in the "coupon" several weeks after and initial implanation. After the valve was removed 6 months later, a slice revealed remants of similar bacterium taken from the patient's heart. However, no live bacteria were found in the patient.

The man in Washington did well immediately after the pig valve was implanted in his heart, said Dr. James A. Curtin, chief of medicine at the Hospital Center.

The baterium was not found until after the implant because the valve must be used as soon as its packaging is opened. It takes several weeks for the bacterium to grow, and thus physicians do not know if the valve is contaminated until long after it has been implanted.

In May, said Curtin, the patient as readmitted to the hospital with cardiac insufficiency. His heart was not doing its job.

"We tried to culture the organism from the patient's blood," said Curtin, "but we couldn't do it . . . Prior to surgery we started him on some antibiotics, which may have had some effect on the growth of the organism.

"At the time of surgery (to remove the infected pig valve and replace it with a man-made valve) there was some infected material removed from the ring of the aorta where the valve rests. The valve itself was intact," said Curtin, but there were abuses, on disease-created spaces around the valve.

Curtin said the evidence suggests the antibiotics might have killed off the bacterium, making it impossible for hospital investigators to find the bacterium in the patient.

Tascom of Hancock said the patient was suffering from a major heart infection prior to the implanatation of the porcine valve, and said the second infection may well have resulted from the original infection, and not from the valve.

Curtin responded to that explanation by saying that the original infection of the heart was caused by a strep bacterium, and the infection was wiped out prior to the first surgery. The second infection, he said, was clearly caused by a bacterium similar to that found on the valve "coupon."

In a letter to the pretigious New England Journal of Medicine, Curtin and a group of his colleagues at the Hospital Center say their findings suggest that "the chronicity of this infection and the difficulty in diagnosis suggest that infections with this fastictious organism may go unrecognized for longperiods of time."

Speaking to a reporter, Curtin called the evidence that the valve caused the patient's second infection "very strong but not convlusive."

While Hooten said the CDC is concerned about the potential problem with the valves, he also said that according to "a lot of surgeons," Hancock "has the best" porcine valve on the market.

"It's a good valve, for several reasons," said Hooten. "It cuts down on the need for anti-coagulants," anticlotting medication, "it lasts long, and it's very pliable, and" can be easily implanted in small hearts.