Alternately moderate and confrontational, as befits their political personae, the two women first elected to the Senate in 1992 are central beneficiaries of Tuesday's political earthquake that gave Democrats a monopoly on Capitol Hill.

Republican Sen. George Allen's concession Thursday to Democratic challenger Jim Webb in their close contest in Virginia gave Senate Democrats their 49th seat and, with the backing of independents Joe Lieberman of Connecticut and Bernie Sanders of Vermont, provides them a 51-49 majority in the new Congress.

Nowhere is the change starker than with Boxer's impending chairwomanship of the Environment and Public Works Committee, where she takes the reins from a conservative Republican who thinks global warming is a hoax.

She vowed to push through global warming legislation next year, taking California's landmark model nationwide -- a move Feinstein proposed in a major speech in August in San Francisco.

Boxer, describing global warming as the challenge of this generation, rattled off the potential dire consequences from a projected 3.7-degree rise in the Earth's temperature, including a melting of the polar ice caps and a 20-foot rise in sea levels along California's coasts. She said she would bring "everybody to the table to come up with a sense of legislation ... because time is running out."

Among the Senate's severest critics of Bush, Boxer said the administration had already extended an olive branch, with a top aide from the President's Council on Environmental Quality contacting her staff indicating a willingness to work together.

"In five minutes, (former Defense Secretary) Donald Rumsfeld resigned, and in 10 minutes we got a call on global warming, so change is in the air," Boxer said.

She acknowledged that she may face resistance even from some Democrats in the Senate and House.

"If I had my way, I would go all 100 yards to do what we need to do," Boxer said. "But if people are willing to go 90 or 80 or 70, we'll find out. But the call from the White House means this is a very different world we're living in."

Feinstein, for her part, warned that Bush's new nominee for secretary of defense, Robert Gates, faces a Senate grilling on Iraq.

While Congress will not cut off money for the war, given the presence of U.S. troops there, Feinstein said, "I think there will certainly be hearings and there will certainly be great discussion on what should be done and I think it will begin with confirmation hearings of the nominee for the secretary. He's going to have to put forth in his nomination hearing what he thinks he would do."

Rumsfeld wasn't solely responsible for Iraq policy, Feinstein said, "but he certainly played a big role in it."

"Transformation of the military is Donald Rumsfeld," she said. "Too few troops is Donald Rumsfeld. The taxing now of the U.S. Army is a product of Donald Rumsfeld's policies, so this all has to be changed."

Feinstein said it will be "very interesting to hear what Gates is going to propose. I don't think he can come before this committee as just any peacetime secretary of defense. ... There is a lot of baggage on the table, and that baggage is going to have to be opened and discussed. There is no better place in my view than the confirmation hearing."

Feinstein, who won re-election Tuesday to a third six-year term, outlined a cautious approach on other matters, noting the Senate's close numbers and the power of the filibuster, a blocking maneuver empowering Senate minorities that requires 60 votes to overcome.

"You have to realize that going into a slim majority is not dominant control," Feinstein said. "Dominant control can only come with 60 votes. ... In other words, we can stop something, but you can't necessarily pass something."

Feinstein predicted movement on immigration reform, but said that the Senate bill passed last year is too big and unwieldy and must be pared back, especially its large expansion of visas. She insisted that Bush propose a bill, which he refused to do last year, and she argued that the administration has greater capacity to pull factions together on such a controversial issue.

Boxer also acknowledged the Senate's institutional constraints.

"Look, I said, this isn't going to be a piece of cake," Boxer said. "But I believe we can make progress. It isn't going to be easy, but it's going to be a lot easier than it was before to move forward."

But both California senators said there is a pent-up demand for movement on global warming.

The current chairman of Boxer's Environment and Public Works Committee, Sen. James Inhofe, R-Okla., held just one hearing, whose "star witness was Michael Creighton, who is a novelist, not a scientist." Nonetheless, Boxer has a warm relationship with Inhofe, who she said called her Wednesday to wish her well. "He was very, very sweet," Boxer said.

Feinstein sits on the committees of Judiciary, Appropriations, Energy and Natural Resources, but she may become chairwoman of the Senate Rules Committee, where she plans to propose federal standards for elections. However, she may assume the chair of the Intelligence Committee if Sen. Jay Rockefeller, D-W.Va., takes another post.

Long an advocate of environmental issues, Boxer, who was first elected to office in 1976 as a Marin County supervisor and served 10 years in the House, described her impending chairmanship as "a dream come true for me. This is something that I consider myself blessed with, and I thank the people of this state for keeping their confidence in me all these years."

E-mail Carolyn Lochhead at clochhead@sfchronicle.com.