Adams died at his home in Stevensville, Md., after a struggle with Parkinson's Disease (search), said Ellen Globokar, who was his staff chief in the Senate.
Adams, a Democrat, represented Washington state in the U.S. House of Representatives from 1965 to 1977 before becoming transportation secretary in the Carter administration.
He went on to unseat Republican Sen. Slade Gorton (search) in 1986, but declined to seek re-election in 1992 after eight women told The Seattle Times that Adams had harassed them. Adams denied the allegations.
"There was never any harassment. There was never any threat. There was never any of these things that were stated in the article," he said.
A previous sexual misconduct allegation had made Adams one of the Senate's most vulnerable Democrats. Adams also denied that allegation.
A former U.S. attorney for the Western District of Washington, Adams was elected to Congress in 1964 and rose to chairman of the Budget Committee before accepting President Carter's offer to become head of the Transportation Department.
He served two years in the Cabinet, then returned to Washington state to resume his law practice.
He made a successful comeback to politics in 1986, defeating Gorton in a closely contested race.
State Democratic Chairman Paul Berendt said the state mourns the passing of a Democratic stalwart.
"Adams was a giant when it came to addressing the complex transportation needs of the region," he said. "He was instrumental in building up the aerospace infrastructure of this region, as well as our ports and our dominance as a trading center."
As a Democrat, Adams "will always be remembered fondly as a 'giant-killer' who defeated Slade Gorton" in the 1986 election, Berendt said. "It is very sad he has passed away, and our thoughts are with his family."