NASA chief James M. Beggs, General Dynamics Corp. and three of its executives pleaded not guilty to charges of plotting to hide cost overruns on a prototype of the Sgt. York antiaircraft gun.

"I plead not guilty to each count," Beggs, a former company executive, told U.S. District Court Judge Ferdinand F. Fernandez.

The indictment alleges that the defendants conspired to hide $7.5 million in company losses on a $41 million Sgt. York prototype by charging expenses to other government-funded accounts between 1978 and 1981, resulting in a $3.2 million loss to the government.

Fernandez scheduled a trial to begin April 8, although prosecutor Randy I. Bellows said the case was too complex to be heard so quickly. Bellows said the government had 2.7 million documents to review.

Thomas P. Sullivan, lawyer for General Dynamics, told Fernandez that the defendants wanted the trial to begin in the spring because a government suspension of most contracts with the company until the case is resolved has put the defense contractor "in a real serious bind."

"This company could be literally . . . put out of business by this suspension," Sullivan said.

Attorneys estimated the trial could take more than 12 weeks, with Bellows saying he would call at least 70 witnesses.

At a bail hearing earlier in the day, U.S. Magistrate Volney Brown Jr., citing conflicts of interest, disqualified himself from the case. Brown said he and his wife own several shares of General Dynamics stock.

U.S. Magistrate Venetta S. Tassopulos presided in his place and approved $5,000 bail for each.