President Bush chose Richard Myers as the new chairman of the Joint Chiefs of Staff — and immediately tasked the Air Force general with encouraging Congress to finance high-tech upgrades for the armed forces.

Bush said Friday that he would nominate Myers, Joint Chiefs vice chairman and the former head of U.S. Space Command, as chairman of the Joint Chiefs of Staff. Bush also nominated Marine Gen. Pete Pace, head of the U.S. Southern Command, to succeed Myers as vice chairman.

Myers, 59, is the first Air Force officer selected for the top Joint Chiefs post in nearly 20 years; Air Force Gen. David Jones was chairman from 1978 to 1982. If confirmed by the Senate, Myers will replace Army Gen. Henry H. Shelton, who steps down Sept. 30.

Shelton said in a statement that Myers has "the heart of a warrior and vision of a leader."

"I have, figuratively and literally, enormous shoes to fill," Myers said. "I am ready to roll up my sleeves and get back to work building the kind of military that President Bush envisions, one that is poised to meet current obligations and emerging threats."

Bush said both Myers and Pace believe in rethinking U.S. defense priorities, and consider it "absolutely necessary" to put adequate funding into research and development.

One of Myers' main jobs, Bush said, would be to ensure that Congress understands "why we are asking for monies for certain force sizes, and how it relates to keeping the national security of the country."

"General Myers is a man of steady resolve and determined leadership," Bush said. "He is someone who understands that the strengths of America's armed forces are our people and our technological superiority, and we must invest in both."

Bush announced the selection at a news conference held at a community center close to his ranch, where he has been vacationing all month. He met beforehand with Myers and Defense Secretary Donald H. Rumsfeld for an update on continuing efforts to overhaul the nation's military.

"Change is hard, and changing so vital an institution as the U.S. Department of Defense is not undertaken lightly," Rumsfeld said.

Bush said Rumsfeld's review includes assessing the threats — real and perceived — of rogue nations and setting defense spending priorities accordingly, starting with the $8 billion Bush has earmarked for developing a missile defense shield and other military priorities.

"We're going to stand our ground and say the $8 billion ... is the right amount of money," Bush said. "Our budget reflects the need to fully explore and, at the same time, make sure that today's military can fulfill the missions."

Bush said the United States cannot afford every weapons system that is "being designed or thought about" by Pentagon researchers. "There are many good ideas, but this administration is going to have to winnow them down," he said. "And when we make decisions, they will fit into a strategic plan."

The nomination of Myers, a supporter of anti-missile systems, comes as the Bush administration is stepping up its bid to develop a missile defense system, and possibly withdraw from the 1972 Anti-Ballistic Missile Treaty.

Bush told reporters Thursday that he has no specific timetable for withdrawing from the treaty.