"I am suffering from a disease known as frontotemporal lobar degeneration," Domenici explained during his announcement at the the Albuquerque grade school he attended as a child. "This disease is progressive and incurable."
Domenici, 75, had hinted he would run for re-election despite some criticism of his role in the controversial firings of U.S. attorneys.
In a statement released by the White House, President George Bush said Domenici "has helped improve the lives of millions of Americans and made our country safer."
Calling him a friend, Energy Secretary Samuel Bodman said Domenici championed the passage of the Energy Policy Act of 2005, "our nation’s first comprehensive energy legislation in more than a decade."
New Mexico Gov. Bill Richardson declared Thursday as "Senator Pete V. Domenici Day," the Las Cruces Sun-News reported.
"I am honored to declare Senator Pete V. Domenici Day in honor of an extraordinary career, a career that has been dedicated to the people of New Mexico," said Richardson, a candidate for the Democratic presidential nomination.