In a continuing probe of corruption in the Federal Highway Administration, a senior engineer at the agency and his wife have been indicted on charges of taking bribes, paying kickbacks and rigging contract bids worth millions of dollars over a five-year period.

James Clark, 47, of Herndon, and his wife, Brenda Clark, 41, amassed more than $170,000 in personal loans and consulting fees from private firms in return for helping them obtain lucrative government contracts, officials said yesterday. The two were charged in a four-count indictment issued Thursday by a federal grand jury in Alexandria. Neither has been arrested.

Reached at the couple's home in Herndon, Brenda Clark denied the charges and said she was unaware that an indictment had been issued. She declined further comment.

Officials at the Federal Highway Administration said James Clark no longer works there but declined to elaborate. They said he worked at the agency for 17 years, most recently as a highway engineer at its research center in McLean. The indictment described him as a "contracting official" who oversaw the awarding of millions of dollars in federal contracts for the agency, a division of the U.S. Department of Transportation.

The indictment charges that Brenda Clark, who was not a federal employee, benefited from consulting contracts given to her by private firms that received large federal contracts from her husband. Brenda Clark had no training or expertise in transportation or engineering, the indictment says.

In another case last year, Alberto Santiago, also a top Federal Highway Administration contracting official from Herndon, pleaded guilty to conspiracy, bribery and laundering money and has been sentenced to three years in prison. Two others--Hobih Chen, the owner of Viggen Corp., a Northern Virginia traffic engineering firm, and Ajay Rathi, an employee of the Oak Ridge National Laboratory in Tennessee--also were charged in the case.

Although Clark formerly was Santiago's deputy, Clark's alleged corruption scheme apparently was separate, said Jeff Nelligan, a spokesman for the Transportation Department inspector general's office, which conducted the two-year investigation with the FBI.

"There was no relationship between the two," he said. He declined to say what had triggered the investigation of Clark.

The latest indictment "is part of a continuing investigation into corruption at the Federal Highway Administration," the Justice Department said.

In all, the five who have pleaded guilty or have been charged received at least $320,000 in payoffs, Nelligan said.

Among those involved in the conspiracy with the Clarks were a program manager in the Oak Ridge National Laboratory's Center for Transportation Analysis, a private corporation based in Colorado Springs, another unidentified private contractor, Brenda Clark's brother and at least four intermediaries who channeled illegal consulting fees between the companies and the Clarks, the indictment says. Investigators would not identify any of the other alleged conspirators.

In 1997, the indictment alleges, James Clark used his position to rig the bidding on a $19 million Federal Highway Administration contract so that it would be awarded to a firm identified only as "Contractor A."

If convicted, James Clark faces up to 75 years in prison and $2 million in fines, while Brenda Clark faces up to 30 years and more than $1 million in fines.