Prospects for ending the 19-day doctors' strike at Group Health Association took a turn for the worse yesterday as negotiations broke off over a GHA threat to discipline up to nine doctors who allegedly failed to honor a prestrike agreement to treat certain patients.

Tense bargaining at the Federal Mediation and Conciliation Service broke down over the disciplinary issue, and 50 to 100 strikers and supporters held a protest rally at noon outside GHA's main District facility at 2121 Pennsylvania Ave. NW.

The 145,000-member health maintenance organization was nearing a settlement late Thursday night with the Capitol Alliance of Physicians on the basic issue involving proposed changes in doctors' office hours, officials said.

But a GHA management proposal to discipline and possibly fire doctors short-circuited the agreement, according to Dr. Nieves M. Zaldivar, president of the 160-member union.

"Our members are unanimous and angry," she said after a meeting of about 100 doctors at George Washington University. "We were ready to wrap it up, but they threw this discipline proposal on the table and blew it. We are not going back to work if anybody is being hung" over alleged strike-related infractions.

GHA director Dr. Robert Rosenberg said last night that the possible discipline involves complaints from patients or nonstriking doctors about physicians who "either did not respond to emergencies or canceled scheduled surgery." He said GHA is not proposing firings, but suspensions in three "serious" cases.

The union and GHA had an agreement before the strike that doctors would continue handling emergencies, childbirth and certain hospital visits. Dr. Zaldivar said GHA never raised complaints until Thursday night at the bargaining table.

A spokesman for the federal mediation service said last night that talks are expected to resume today.

The primary issue since the strike began March 3 has been GHA's plan to require doctors to increase by several hours a week the amount of time spent on office visits. GHA management linked the plan to an incentive pay system that would increase wages for doctors attaining certain numbers of "encounter units," which are patient-doctor contacts.

The member-owned nonprofit GHA described the plan as an efficiency and cost-saving move to assure patients more access to doctors. But the doctors said it would hurt patient care by forcing them to speed up visits and reduce time spent on other duties such as visiting hospital and nursing home patients.

GHA physicians earn an average of $91,000 and are required to work 35 hours a week. Twenty to 35 hours must be spent on office visits, depending on the doctor's specialty, under the existing union contract. While GHA management acknowledged that many doctors already work considerably more than 35 hours, they said they proposed increasing the minimum office hours because some doctors were not available often enough to patients. A compromise agreement was being fashioned when the talks broke off.