The balance of power in the Senate will not change because of the death of Republican Sen. Craig Thomas because state law in Wyoming requires the governor to let the party with the vacancy recommend a successor.

Thomas, a conservative, died after a fight with leukemia that was diagnosed last year just as he was elected for a third term. He was 74.

The senator's family said he died Monday evening at National Naval Medical Center in Bethesda, Md. The family had said earlier in the day that his cancer had been resistant to a second round of chemotherapy for acute myeloid leukemia.

He had also developed an infection, his family said.

In accordance with state law, Gov. Dave Freudenthal, a Democrat, will appoint a successor from one of three finalists chosen by the state Republican party.

Freudenthal called Thomas' death "a very big loss to the people of this state," saying "he carried the values that we treasure in Wyoming to Washington and had many successes."

Peggy Nighswonger, Wyoming's elections director, said the Republican party will have 15 days to convene and choose the nominees after it is officially notified by the governor of Thomas' death. Once the governor receives the names from the party, he has five days to choose one.

The new senator will serve until the next general election in 2008, when a special election will determine who completes Thomas's term, which runs through 2012.

Democrats and Republicans each have 49 members of the 100-member Senate. But two independents vote and organize with Democrats, giving them the slim majority they presently hold. Sen. Tim Johnson, D-S.D., has been recovering from major illness and has not participated in Senate activities in months.

Thomas was hospitalized with pneumonia just before the 2006 election, but won with 70 percent of the vote, monitoring the election from his hospital bed.

Two days after the election, Thomas announced that he had just been diagnosed with leukemia.

President Bush called Thomas "a man of character and integrity known for his devotion to the values he shared with the people of Wyoming."

"He leaves a lasting legacy as a guardian of Wyoming's lands and resources and our country's National Parks," Bush said.

Vice President Dick Cheney, who held Wyoming's only House seat before Thomas replaced him in 1989, called Thomas a friend and said "he never let us down."

"Even in a time of serious illness Craig was faithful to his duties in the United States Senate," Cheney said. "His passing represents a profound loss to the Senate, to Wyoming, and to America."

"Wyoming had no greater advocate, taxpayers had no greater watchdog, and rural America had no greater defender than Craig Thomas," said Senate Republican Leader Mitch McConnell said Monday night.

Thomas was a low-key lawmaker who reliably represented the interests of his conservative state, often becoming involved in public lands issues. He worked in behind-the-scenes posts to oversee national parks.

"The Senate will not be the same," said Republican Mike Enzi, Wyoming's other senator.

The state's only member of the House, Republican Barbara Cubin, said Thomas was "a trusted colleague and a true friend."

Wyoming Democratic Party Chairman John Millin said Thomas brought "dignity and thoughtfulness" to the political process, and Wyoming GOP Chairman Fred Parady called Thomas a "true champion."

Thomas entered Congress in a special election in 1989 to replace Cheney when he was named defense secretary by the first President Bush. Thomas won that race with 52 percent of the vote.

In 1994, Thomas won his first Senate race by beating former Gov. Mike Sullivan and was re-elected with 74 percent of the vote in 2000.

Thomas had previously served five years in the Wyoming Legislature.

He was born in Cody, Wyo., and was raised on a ranch. He graduated from the University of Wyoming with a degree in agriculture, then served four years in the U.S. Marines.

He is survived by his wife, Susan, and four children.