Physicians employed by the 112,000-member Group Health Association, the largest prepaid health care plan in the Washington area, have threatened to strike Jan. 12 if they have not reached a contract agreement by that date.

Such a strike would be Group Health's second in 20 months. The GHA doctors stayed off the job for 11 days in the spring of 1978. It was the nation's first strike by fully trained physicians.

Unlike subscribers to conventional insurance plans, GHA's members pay the organization an annual fee and then go to one of its physicians for all their health care needs, from basic physicial exams through surgery.

Two major issues repeatedly separate the two sides. The first is the question of whether GHA physicians should be allowed to have patients who are not members of the organization. The second centers on how many patients a physician should be required to see in a day.

Dr. Edward Himnar, GHA executive director, said he feels that "by hard bargaining, we can get a contract."

But Dr. Norman Lieberman, president of the physicians' union said he is pessimistic about the possibility of avoiding a strike. Negotiations began in the fall and are continuing despite the expiration of the contract on Dec. 31.

Both the union's leadership and the GHA board of directors -- which must ratify any contract -- are virtually unchanged since 1978. And the major issues now are those that confounded the two sides then.

According to the union, after GHA turned down a demand of wage increases of roughly 8 percent a year -- on an average physician's salary of $58,513 -- the union "reluctantly agreed" to accept 4 percent a year if the physicians could supplement their incomes by seeing patients on the outside.

According to Lieberman, last Saturday night the union and GHA negotiators reached a tentative agreement, which was taken to the organization's board and then rejected.

Officials of Group Health have said simply that four "proposals were taken to the board and the board immediately rejected any outside practice" without considering the rest of the agreement.

Board chairman Harold Wool said yesterday in an interview that board members feel there is no room for compromise on the outside practice question. The board took the same stand in 1978.

Wool said that GHA members have felt since its founding in the 1930s that physicians employed by Group Health should give its patients their undivided attention.

The physicians said they have proposed that the medical director of the organization -- a management official -- be given authority to determine if a physician's outside work interferes with the care of GHA patients, and to order an end to that extra work if it does.

The other basic issue is productivity. Management, which means the representatives of GHA's subscribers, takes the position that physicians must see more patients in order to hold down costs and eliminate the need to hire more physicians.

According to Wool there has been a "significant" decrease in physician productivity since the signing of the last contract. He would not elaborate, saying that the question should be settled "at the bargaining table" and not in the press.

Lieberman, however, said that GHA is demanding that physicians care for "one patient every 12 minutes in some departments." In the dermatology department, he said, where physicians now see a patient every 15 minutes they would be required to see them every 12 instead.

Lieberman, an internist, said he now sees a patient about every 20 minutes "and I'm going to hurt a patient if I'm forced to see more patients."