If there was optimism on Capitol Hill about the Andrews Air Force Base budget talks, little of it crept into Room 311 of the Cannon House Office Building yesterday morning.

A parade of witnesses went before a joint hearing of two Civil Service subcommittees to speak in dark, dire terms of what would happen to the nation if the federal government makes good on its threat to begin laying off workers next month. The layoffs would produce "cataclysmic results," said the National Treasury Employees Union in a statement that warned of delays in air travel, Social Security payments and vaccinations for children.

Yesterday, the witnesses and members of the subcommittees seemed to agree with the union that the Washington area would suffer if the government presses ahead with its plan to force many of the region's 360,000 federal workers to take "unpaid leave" beginning Oct. 1, the start of fiscal 1991.

Shortages of Agriculture Department inspectors would force Giant Food stores to run short of eggs and poultry products, Rep. Constance A. Morella (R-Md.) cautioned. Montgomery County Economic Development director Dyan Lingle Brasington said home mortgage defaults and individual bankruptcies would soar and there would be "a serious diminishing of our quality of life in general."

Thomas C. Komarek, an assistant secretary of labor, said the impact on his department "would be staggering," causing "irreparable harm to our programs and the people we are here to serve: the American worker."

Even an official from the Office of Personnel Management, which had declared furloughs are the only way most agencies can achieve cuts of the magnitude they will have to make under the Gramm-Rudman-Hollings law, agreed that it was "the most Draconian" of personnel actions.

While the two panels were considering furloughs, congressional and Bush administration negotiators at Andrews were reported moving toward an agreement on a budget proposal that, if approved by Congress, might forestall the layoffs.

But John N. Sturdivant, president of the American Federation of Government Employees, said yesterday afternoon that federal workers would not emerge unharmed under the new fiscal curbs.

"We understand that this budget agreement would mean that some 25 percent of all the cuts being made at the summit would come out of the hides of federal and postal workers and retirees," said Studivant, head of the largest federal worker union.

A draft document circulated by Democratic leaders indicated budget negotiators were prepared to cut $3.8 billion in various federal employee pay and benefit programs. Over a five-year period, the cuts would total $37.3 billion of the $135.4 billion in anticipated domestic budget savings.

Congressional negotiators appear to have targeted federal employee benefits and the Medicare health insurance program for 75 percent of the budget cuts through fiscal 1995.

Specific cuts would:

Eliminate the lump sum payment program for retiring employees. Government workers currently can receive 50 percent of the money they contributed to their pension plan on retirement and the balance the following year. By eliminating the program, budget negotiators estimate they can save $8.5 billion during the next five years.

Support President Bush's plan to freeze cost-of-living allowance (COLA) payments for government employees in fiscal 1991 and then set the allowance at 1 percent below the annual rise in the government's cost of living index. This would save $17.1 billion through fiscal 1995.

Eliminate cost-of-living payments on the pensions of members of the military who retire before age 62. Budget negotiators plan to continue COLA payments for civilian retirees, sources said yesterday.

Cut at least $400 million a year from the Federal Employee Health Benefit program. Sources familiar with the budget proposal said this would result in an increase in health premiums for federal employees. The cut is lumped together with unspecified cuts in the U.S. Postal Service budget totaling $6.8 billion through fiscal 1995.

Rep. Steny H. Hoyer (D-Md.), who testified yesterday, said the hearing should warn the negotiators not to use federal workers "as the pocketbook of first resort."

Hoyer objected to a proposal by Rep. Tom McMillen (D-Md.) to enact legislation to force presidential appointees to take unpaid leave along with the civil servants. "The issue is not to make them {the furloughs} fairer," Hoyer said. The objective was to eliminate furloughs, he said.