The former chairman of a bankrupt Virginia real estate investment firm, known as National Commercial Credit Corp., pleaded guilty yesterday to a federal charge of engaging in securities fraud.

The guilty plea by Harry Koenigsberg, 73, a former McLean resident, represented the first criminal prosecution to result from an investigation by the Securities and Exchange Commission and the Justice Department.

Koenigsberg entered his plea to a single misdemeanor count of defrauding investors yesterday morning in U.S. District Court in Alexandria. In exchange for the guilty plea, Assistant U.S. Attorney Theodore S. Greenberg said federal prosecutors had agreed not bring any further charges against Koenigsberg.

Judge Albert V. Bryan Jr. set sentencing for Oct. 20, Koenigsberg faces a maximum fine of $10,000.

More than 100 investors, including many present and former Virginia residents, appear to have lost hunderds of thousands of dollars through purchasing National Commercial Credit Corp's bonds and notes, according to court records.

A central figure in the federal investigation of the NCCC bankruptcy in Cortes W. Randell, a businessman who gained considerable notoriety when he went to prison in 1975 in the National Student Marketing Corp, scandal. Randell, once a reputed financial whiz kid, pleaded guilty to stock fraud charges in the student marketing scheme.

Last year, Randell and three associates in National Commercial Credit Corp. were accused of fraud in a civil complaint filed by the SEC. They were alleged to have "ravaged" NCCC of its assets. Randell later signed a consent decree in which he neither admitted nor denied guilt. Koenigsberg was not charged in the SEC complaint.

In a criminal information entered in U.S. District Court yesterday, Koenigsberg was accused of defrauding investors in National Commercial Credit Corp, by selling unsecured notes and failing to inform buyers about indications of the firm's financial weakness.

Among "material facts" Koenigsberg failed to bring to investors' attention, the information alleged, were that the firm had advanced substantial funds to its Florida agent "which were not accounted for," that NCCC's financial condition had been "adversely affected" by these advances, and that Randell, a convicted felon, was a director, "indirect owner" of 25 percent of NCCC's stock and "a controlling person of NCCC."