The Renegotiation Board, the federal watchdog agency that faces extinction next spring, reported yesterday that it earned a "profit" of $28 million on its operations for the fiscal year that ends today.

In a talk to the board's employes, Chairman Goodwin Chase announced that the agency, which reviews defense and space contracts to keep contractors from accumulating excessive profits on their government sales, had recaptured profits totaling $34.4 million during fiscal year 1978.

The board's operting budget for the year was $6 million.

Chase said in an interview after the meeting that about 40 percent of the $34.4 million recovered was determined through agreements with contractors. The remainder involves repayment orders that are being disputed by contractors. These orders can be appealed to the courts.

After a forceful lobbying effort by contractor organizations, Congress this year voted to abolish the board next March 31. The agency's backers say there is little hope of reversing that decision.

Chase noted yesterday that some of the board's most experienced analysts have been leaving for other jobs in recent months. He pleaded with employes to stay with the agency on the chance that its life might be extended.