Washington Hospital Center, the city's largest private hospital, has begun to reduce temporarily it emergency service and to cut in half its capacity to keep patients in the hospital in response to a strike threat by registered nurses.

The strike is scheduled for 7 a.m. Saturday if negotiations, which resumed yesterday for the first time in five months, fail to head it off.

Jane Snyder, a hospital spokeswoman, said the 911-bed hospital has already placed itself on "re-route" status with the city's ambulance service, which means that only patients who could not live long enough to get to another hospital will be brough to the hospital's emergency room.

At the same time, Snder said, hospital officals have already begun shifting patients within the hospital to close down some units, including a 50-bed ophthalmology unit, and to consolidate others.

A total of 425 registered nurses work at the hospital center in nonsupervisory capacities. Officials of the fledgling union representing the nurses predict that about 300 of those nurses will walk out at 7 a.m. Saturday if no agreement is reached by that time between themselves and the hospital.

The hospital center also has about 100 nurses in supervisory roles, and thus would be able to call on a complement of about 225 registered nurses, as compared to the usual 525, if the strike occurs.

Some physicians at the hospital, who have asked that their names not be used, have said they believe the hospital must shut down its entire emergency room operation if it is to deliver quality care during a nursing strike.

"We do not intend to do that," Synder said. She said that hospital officials do not feel such a move is necessary.

The hospital no longer is taking elective admissions involving patients who cannot be discharged later than Friday, Syder said. She said moves are also under way to make sure that any patient who can be discharged before Saturday morning will be sent home.

Some patients who cannot be discharged, she said, will be transferred to other hospitals. All this is being done, Syder said, to reduce the number of patients in the hospital because "the decision that we made was to deliver the best quality of care to the smaller number of patients."

The Washington Hospital Center is almost twice as large as any of the city's other private hospitals, with 911 beds compared to 430 at Georgetown, 511 at George Washington and 450 at Greater Southeast Community Hospital.

While its emergency room is by no means the city's busiest - a title held by D.C. General with about 100,000 emergency room visits a year - its 44,000 annual emergency room visits make it twice as busy as Georgetown and just a bit busier than George Washington, which has about 42,000 such visits a year.

Meanwhile, negotiations between the nurses and the hospital resumed yesterday for the first time since last December. The two sides met for two hours under the auspices of the Federal Mediation and Conciliation Service, and are scheduled to meet again at 10 a.m. today.

While the two sides are not far apart on the wage issue, they are speaking a different language on such questions as scheduling of shifts, granting of maternity and eductional leave, procedures regarding performance evaluations and sick leave and vacation.

A major complicating factor in the situation is that last month the hospital unilaterally withdrew recognition of the union as the bargaining agent for thenurses. That issue is now before the National Labor Relations Board in an action separate from the contract negotiations.

Specifically, the nurses are demanding:

A closed shop. That means all registered nurses at the hospital would have to belong to the union, a provision the hospital is flatly refusing to accept.

The right to work only day shifts and the right to request certain shifts. The hospital is insisting on setting schedules, and would honor requests only for night shifts.

An increase in the number of days of vacation and sick leave.The nurses now receive 19 days of combined leave in their first two years and up to 29 days after nine years. That would give a nurse four weeks of vacation and nine days of sick leave. The hospital has offered one additional day of leave.

One week's paid education leave a year. The hospital has offered one day in the first year and two in the second, with no accumulation.

The right to file grievances if the nurses disagree with work evaluations. The hospital would allow nurses to add their written comments to the evaluations.

A strike by the hospital center nurses would be the sedand strike by health professionals in the city in the past 45 days, Physicians at the Group Health Association struck last month for 11 days.