A Virginia physician is establishing a telephone service to provide afterhours medical advice and prescriptions to patients he and his colleagues have never seen or examined. The only requirement is that the patients must hold one of three major credit cards.

Dr. David T. Schwartz, a Woodbridge urologist and assistant clinical professor at the George Washington University School of Medicine, said he is establishing "on call" to fill what he sees as a need for evening and weekened medical sevice.

Two leaders of the Virginia and District of Columbia medical societies, however, said they are concerned about the ethical and medical implications of this kind of service.

Schwartz said telephone calls to "on call" will be handled by physicians trained in internal medicine, although he said that "some" of the four doctors involved in the project are still in their residency at Georgetown University Medical Center.

A spokeswoman for Georgetown said officials there would not comment on the service, except to ask: "We'd like to know who the residents are."

"This is not intended to be continuous long-range or short-range medical care," said Schwartz, who was trained at Columbia University's College of Physicians and Surgeons and two prestiogious New York City hospitals.

"This is specifically designed for that after-hours situation where the doctor's office is closed, where a patient needs advice and may or may nor need to be seen."

Dr. Raymond Scalettar, president the Medical Society of the District of Columbia, called the service "so overtly commercial it certainly doesn't smack in any sense of the practice of medicine in which someone should be seen, spoken to, and examined if the circumstances warrant it.

"But to reduce the practice of medicine to . . . a telephone call, and letting it go at that, would seem to me to be not in the best interests of the patient," said Scalettar, reached by telephone at the American Medical Association convention in Chicago. "One would worry about the possibility of misdiagnosis . . . or prescribing erroneous medications . . ."

"The question comes up, how can you prescribe over the phone," said Schwartz "What you're doing" - after first requesting a credit card number and receiving an authorization from the card company - "on the basis of the history you're getting, is first making the decision whether you can do anything over the phone.

"If you can't you tell them to get seen" by a physician. "You exclude the things that require that they be seen right away. You advise and give prescriptions only on a likelihood basis. These things are done with the proviso that you tell the patient, 'it this doesn't work, call back or see a doctor.'"

"Nobody's saying this is as good as seeing you face-to-face," said Schwartz. "This is done on the basis of 12 years' experience with covered service, with doctors" taking care of each other's patients on weekends and in the evening.

Of those whom doctors care for over the phone, said Schwartz, "maybe 5 per cent need to be hospitalized, maybe 20 per cent really need to be seen, but with two-thirds of the people, it was perfectly appropriate" to provide telephone advice and medication.

"It smells bad, this kind of thing always smells bad," said Dr. H.C. Kuykendall, a member of the 10-physician governing body of the Medical Society of Virginia.

"In medicine we've got a problem at the moment, as recently it's been declared legal (for professionals) to advertise. We have not yet been able to grapple sufficiently with this question to be able to say, all right, regardless of what is legal, what is ethical is another matter . . ."

Schwartz, who did not seek out media attention, said that he is not advertising, and said that "on call" brochures will be placed in the offices of physicians who want to make the service available to their patients.

However, said Kuykendall, "I feel sure that what Schwartz is doing is not illegal. I think it's sort of marginal thing. It's grayish sort of area.