Senator Robert Byrd (D-WV), chairman of the Senate Appropriations Committee, awaits the start of a committee meeting on Capitol Hill in Washington May 15, 2008. REUTERS/Kevin Lamarque

WASHINGTON (Reuters) - Sen. Robert Byrd, the oldest member of the U.S. Senate and a fierce opponent of the Iraq war, was taken to a Washington-area hospital for observation on Monday after a caregiver noticed that he was lethargic, a spokesman for the West Virginia Democrat said.

Byrd, 90, was at work in the Senate earlier in the day and had gone home where his caregiver grew concerned about his condition, spokesman Jesse Jacobs said.

“She took his temperature and discovered that he had a fever. It was significant enough that his doctor suggested he go into the hospital for observation,” Jacobs said.

Byrd was expected to be kept overnight, the spokesman said.

As chairman of the Senate Appropriations Committee, Byrd has been one of several leading Democrats in Congress trying to bring the Iraq war to an end by tying troop withdrawals to war funds. Unlike many of his fellow Democrats, Byrd opposed the 2003 U.S. attack on Iraq from the outset.

Byrd was last elected to a six-year term in 2006. Democrats hold a narrow majority in the Senate and will try to increase their numbers in November’s election, when one-third of the 100 Senate seats will be up for grabs.

Byrd first won election to the Senate in 1958.