St. Elizabeths Hospital must reduce its staff by 906 employes--250 more than originally thought--and severely cut a dozen programs in order to comply with a federal order to save $25 million, steps that will cause it to lose its accreditation within a year, the hospital's superintendent said yesterday.

In a cost-savings plan submitted to Reagan administration officials, Dr. William Dobbs, superintendent of the federal psychiatric hospital, said the hospital must lose 906 employes by Dec. 1 if neither the District or federal governments supplies extra money for the hospital.

When federal officials ordered the plan prepared, they estimated that around 650 employes would have to lose their jobs.

In an interview yesterday, Dobbs said the more severe cuts and layoffs are necessary because the $25 million cutback ordered by the federal government will also cost the hospital $2.3 million in lost reimbursements from Medicare. The Medicare payments are partly dependent on the institution's overall budget.

Under Dobbs' plan, about 750 of the hospital's 2,900 employes would be fired and the remaining 156 would be lost through early retirements and attrition. The reductions-in-force would cost $7 million to accomplish, an amount that would be paid by the federal government, according to the plan. All patient-workers would be fired and the hospital's medical training programs and alcohol and drug abuse treatment programs would be curtailed.

The plan states that the cuts will cause the hospital's "good" patient care to slip to "minimally adequate" care, resulting in a loss of accreditation which would cause the hospital to lose up to $30 million in Medicare and Medicaid reimbursements.

"It seems incredible that we would keep it accreditation ," Dobbs said in an interview yesterday. "If we lost Medicare and Medicaid, that would just about kill us off."

The hospital won full accreditation from the Joint Commission on Hospital Accreditation in October 1981. Inspectors from the monitoring firm were not scheduled to make a re-inspection until next July, but drastic changes such as large staff reductions often prompt a new evaluation. The accreditation is necessary to participate in several government medical programs.

Dobbs, who had intended to retire Oct. l after 27 years at St. Elizabeths, said he has agreed to stay on through 1983 and possibly into the new year.

"I'm not going to walk out with the hospital in this fix," he said.

The 127-year-old hospital's current problem dates back 20 years, when the federal government began efforts to transfer the facility to the District government. At issue is the fact that a majority of the patients are District residents, while the federal government pays two-thirds of its costs.

Two years ago, the U.S. Office of Management and Budget instituted a 10-year-program to transfer the hospital, beginning with steep reductions in the amount of money the federal government supplied for the hospital's $143 million budget.

The transfer attempts have not succeeded, although the District has increased its share of the hospital's budget from $24.7 million to $29 million for the coming year.

The federal government, which is paying $62.7 million for the hospital in the coming year, wanted the District to increase its share to $54.5 million, an amount District officials say they cannot afford. The gap between the two budget amounts leaves the hospital budget $25 million short.

Last year a similar situation developed and the Congress made up the difference by adding money to the District's budget. This year, that has not happened.

Congress adjourned without finally settling the issue and the conference committee on the District budget is not expected until late September. Because the hospital faces continued federal reductions in the coming years, at least part of the cost-saving plan will be imposed even if Congress again appropriates more money, Dobbs said.

Under the cost-saving plan, all employe travel would be abolished, and overtime, equipment and supplies would be reduced. Programs for Hispanic and deaf patients would be eliminated, as well as an in-hospital school for children. A special unit to treat women criminals would be abolished, meaning these patients would no longer be separated from the rest of the mentally ill patients, Dobbs said.

The cutbacks will mean a loss of counselors to prepare patients for life outside the hospital, which will "increase the number, frequency and duration of readmissions, a phenomenon the hospital has been quite successful in avoiding in recent years," the plan states.

The plan was submitted to the federal Alcohol, Drug Abuse and Mental Health Administration, which oversees the hospital. Its deputy director, Robert Trachtenburg, said cutbacks must be instituted if additional money is not appropriated by Oct. 1.