Striking nurses, supported by physicians in sympathy with their demands for higher wages and additional staffing, yesterday forced Group Health Association, the metropolitan area's largest medical care cooperative, to postpone routine patient visits and limit care to more serious cases.

Representatives of the 80-member Registered Nurses and Physical Therapists Association, which went on strike Thursday, met for the second time with GHA negotiators and federal mediators. At issue is the nurses' demand for what their president, Denise Mullane, termed "parity with the area."

Mullane refused to discuss specifics of salary demands. However, GHA executive director Dr. Edward J. Hinman said that negotiations began Thursday with the nurses demanding a 41 percent wage increase over three years and GHA offering a 29.4 percent increase over the next two.

Average yearly salaries for registered nurses at GHA range between $14,627 and $19,000.

With all the nurses on strike and about 80 percent of the 105-member Capital Alliance of Physicians staying away, emergencies were handled by those physicians who crossed the picket lines, Hinman said.

GHA, which runs health care centers in Washington, Annandale, Marlow Heights, Hyattsville and Rockville, has 112,000 members and ordinarily handles about 2,000 cases a day. Hinman said he was unable to say what the case load was yesterday.

Joan Rowan, vice president of the nurses' union, said that despite earlier contentions by Hinman that staffing demands were not a real issue, "adequate staffing is critical to good care and the only way to get it is to strike."

Not only were nurses so overworked at the GHA centers that they couldn't take lunch hours, Rowan said, "but, for example, we don't even have time to sit down with a patient who's just beeen told he has diabetes and explain the implications to him."

According to GHA communications director Bettie Payne, the organization has seven registered nurses for every 10,000 member-patients.

"That's not what's keeping us apart," Hinman said. "We're better staffed with nurses than any of the seven HMOs (health maintenance organizations) in the country."