WASHINGTON>> Sen. Robert C. Byrd, who holds the record as the longest-serving member of Congress, is seriously ill in a Washington-area hospital, his office said Sunday.

The 92-year-old West Virginia Democrat has been in the hospital since late last week, his office said in a statement. At first Byrd was believed to be suffering from heat exhaustion and severe dehydration, the statement said, but other medical conditions have developed. His condition was described as serious.

The statement did not name the hospital.

In November, Byrd broke the record for congressional service that had been set by Democrat Carl Hayden of Arizona, who served in the House and Senate from 1912 to 1969.

Byrd began his career in Washington in 1952 with his election to the House. His elevation to the Senate came six years later.

Byrd has been in frail health in recent years and was hospitalized three times in 2009. He has been confined to a wheelchair, but was present and voted "yes" for final Senate passage of the health care reform bill in March.

"He’s our champion," West Virginia Gov. Joe Manchin said Sunday. "Our prayers are with him."

During previous health problems, "he’s always rallied, and I’m depending on him to rally again," Manchin said.

Byrd has been the longest-serving senator since June 2006 and was elected to an unprecedented ninth term in November 2006. His colleagues have elected him to more leadership positions than any senator in history. He has cast more than 18,000 votes and has a nearly 98 percent attendance record over the course of his career.

His wife, Erma, died in 2006.