Mr. Cheney has played a major role in cabinet selections, but never more so than with Mr. Rumsfeld. It was Mr. Rumsfeld who brought Mr. Cheney into the Ford White House as a deputy chief of staff, and who has been the vice president-elect's prototype of a political executive ever since.

The two men share remarkably similar résumés — congressman, White House chief of staff, secretary of defense and corporate chief executive — as well as a results-driven, no- nonsense management style. Mr. Cheney was the last Republican secretary of defense, serving under Mr. Bush's father, President George Bush, and had a very clear idea of the ideal candidate for the job: qualifications that Mr. Rumsfeld fit to a T.

The only trick was persuading Mr. Rumsfeld to serve again, a challenge that Mr. Cheney took on over the past several days, transition aides said.

"I tell you, this has all happened very rapidly," Mr. Rumsfeld, who has been working as an independent consultant, told reporters.

Mr. Rumsfeld, who served as secretary of defense for 14 months from 1975 to 1977, after the withdrawal of American forces from Vietnam, is a skilled bureaucratic infighter who will serve as a complement and counterweight on Mr. Bush's national security team, especially to Gen. Colin L. Powell, the secretary of state-designate.

But he is perhaps best known recently for heading a bipartisan panel in 1998 that concluded that nations like North Korea and Iran could threaten the United States with long- range missiles sooner than American intelligence analysts had predicted. This has led Mr. Rumsfeld to be a leading advocate for missile defenses against such threats. The panel's report became one of the most influential in recent American military planning. Mr. Rumsfeld was among a group of Republican foreign policy luminaries, including Henry A. Kissinger and George P. Shultz, former secretaries of state, who flanked Mr. Bush at a news conference in May when the the Texas governor renewed his pledge to develop robust missile defenses.

With Mr. Rumsfeld's nomination, Mr. Bush has chosen eight members he expects to have in his cabinet. There are 14 statutory cabinet members, but every president can elevate any number of agencies to that level during his term. All of them must be confirmed by the Senate.

Aides said they expected Mr. Bush to make additional personnel announcements on Friday before returning to Texas to celebrate the New Year at his ranch.

Mr. Bush said he hoped to have his cabinet appointments finished by the end of the first week of January, adding with a laugh that he did not want to be held to that deadline.

"Let me just put it to you this way: On Inauguration Day, we will be ready to assume our respective offices," Mr. Bush said.

But the president-elect acknowledged that he was having trouble fulfilling his goal of recruiting a Democrat or two to serve in his cabinet.

"I've talked to some Democrats about whether or not there may be an interest of leaving their current positions," Mr. Bush said. "And most people want to stay in place."

Mr. Bush did make several senior White House staff appointments today. He named Joseph Hagin, a deputy campaign manager, to be deputy chief of staff for operations; and Joshua Bolten, the campaign policy director, to be deputy chief of staff for policy. Ari Fleischer, the campaign and transition spokesman, was named White House press secretary.

Mr. Cheney also announced that two former Pentagon aides would join his White House staff: I. Lewis Libby to be his chief of staff and David Addington to be his counsel.

Explaining why he chose Mr. Rumsfeld, Mr. Bush noted his experience in government and in the corporate world. But he underscored Mr. Rumsfeld's role on the missile-threat panel.

"I felt he did an extraordinary job with a delicate assignment," Mr. Bush said. "He brought people together to understand the realities of the modern world."

Mr. Bush said he would rely on Mr. Rumsfeld to do "a selling job" on Congress to support not only the contentious missile defense proposal, which faces strong opposition from many Democrats as well as foreign allies, but also the costly task of revamping the military to deal with a new security threats, from terrorism to chemical-weapon attacks.

"One of Secretary Rumsfeld's first tasks will be to challenge the status quo inside the Pentagon, to develop a strategy necessary to have a force equipped for warfare of the 21st century," Mr. Bush said.

Mr. Rumsfeld kept his remarks brief and rather broad: "It is clearly not a time at the Pentagon for presiding or calibrating modestly. Rather, we are in a new national security environment. We do need to be arranged to deal with the new threats, not the old ones, with information warfare, missile defense, terrorism, defense of our space assets and the proliferation of weapons of mass destruction throughout the world."

One area that Mr. Rumsfeld said he would not revisit is the military's "don't ask, don't tell" policy on gays in the armed forces.

"That is not an issue that President-elect Bush has discussed in his pronouncements on defense," Mr. Rumsfeld said.

On Capitol Hill, Mr. Rumsfeld's announcement won praise from Democrats and Republicans.

"The nation is fortunate that this experienced, tested, tough-minded `old hand' joins the strong Bush corral for national security," said Senator John W. Warner, a Virginia Republican who heads the Armed Services Committee, which will hold confirmation hearings on Mr. Rumsfeld.

The committee's senior Democrat, Carl Levin of Michigan, called Mr. Rumsfeld "a strong choice."

At today's news conference, Mr. Bush offered insight into how he envisions his national security team to work and what his role will be. When asked how much influence Mr. Cheney and his close friend and ally, General Powell, a former chairman of the Joint Chiefs of Staff, would have at the Pentagon, Mr. Bush said, "I think little."

Then, warming to a subject that he has acknowledged having little expertise in, Mr. Bush continued, referring to Mr. Rumsfeld, "I picked a strong leader who is willing to listen to others but is a decisive leader. General Powell's a strong figure, and Dick Cheney's no shrinking violet. But neither is Don Rumsfeld."