A Belgian national pleaded innocent yesterday to federal charges that be offered up to $500,000 in bribes on behalf of a Soviet company to obtain a secret computer program from a Northern Virginia company.

The man, Marc Andrew DeGeyter, 31, of Schilde, Begium, was indicted last week on eight counts of allegedly trying to buy a secret data management system from Software AG of North America, a Reston-based firm. During the period he allegedly tried to buy the information, from May 1979 to May 18, 1980, DeGeyter claimed to be working on behalf of a Moscow-based trading company called Techmaskbimport, according to court papers.

DeGeyter had been in jail since his arrest May 18 at Kennedy International Airport in New York, when he allegedly handed a $500,000 check to an undercover FBI agent in exchange for two reels of computer tape. cYesterday District Judge Albert V. Bryan Jr. of U.S. District Court in Alexandria reduced DeGeyter's bond from $500,000 to $100,000, but imposed unusual conditions on DeGeyter if he posts the $100,000 bond.

Bryan ordered DeGeyter to stay away from any foreign embassy, consulate, or United Nations office, and to report to the U.S. Marshall service daily if he is released from jail.

Prosecutor Theodore Greenberg opposed the motion to reduce the bond, saying that DeGeyter had attempted to evade federal export laws by trying to send certain goods to the Soviet Union without a license. Greenberg also told Bryan that the $500,000 check DeGeyter allegedly gave the FBI to pay for the computer reels had bounced.

DeGeyter was charged with eight counts of commercial bribery. He faces 40 years in prison and an $80,000 fine if convicted. Bryan set his trial date for July 22.