WASHINGTON—President-elect Barack Obama is facing a Congress with bulked-up Democratic majorities in both the House and Senate to put much of his agenda into law.

Obama will inherit a Congress with Democratic House and Senate majorities comparable to those enjoyed by President Bill Clinton when the party last controlled both Congress and the White House in 1992. While Democrats are eager to churn out the new president’s legislative programs, they’re also anxious to avoid the electoral wipeout that swept them from power in the 1994 congressional elections.

That’s one reason top leaders like House Speaker Nancy Pelosi promise not to lurch to the left and give in to pent-up demands from party liberals.

“The country must be governed from the middle,” Pelosi told reporters Wednesday. “You have to bring people together to reach consensus on solutions that are sustainable and acceptable to the American people.”

One of the complications for Pelosi and Obama is the demise of Republican moderates like Rep. Christopher Shays of Connecticut, who lost his re-election bid.

“Never in modern day history has the Republican Party been more bereft of a center,” said former Rep. Jim Leach of Iowa. “So the center has to come from the Democratic Party.”

There are other reasons too, such as a coalition of Republicans and a few conservative Democrats in the Senate. In the House, a big bloc of moderate-to-conservative “Blue Dog” Democrats also could put the brakes on overreaching by Obama and allies like Pelosi and Senate Majority Leader Harry Reid. But after 14 years of either a Republican-dominated Congress or a Republican president, Democratic Party regulars are under intense pressure to deliver on an agenda they’ve been promising long before Obama announced his bid for the White House.

“I’m not worried about overreaching,” said Rep. Jim McGovern of Massachusetts. “I’m worried about being too timid and too cautious, and not stepping up to the plate and doing what we promised we would do.”

Added Sen. Sherrod Brown of Ohio, “This election ushered in the next progressive era for our nation. From health care to trade to education, progressive values will now be the priority in Washington. It’s time to get to work.”

House Majority Leader Steny Hoyer of Maryland countered that Democrats would impose “self-discipline” because so many House newcomers come from conservative-leaning districts.

“If we focus on the core issues of jobs, of health care, of education, of the environment ... I think we will not make mistakes,” Hoyer said.

Inside Pelosi’s caucus of House Democrats, whose numbers will swell to at least 254 from 235 now, some tensions are already apparent.

Rep. Henry Waxman of California, a liberal Pelosi ally, launched a bid to challenge 82-year-old Rep. John Dingell, of Michigan, for the chairmanship of the influential House Energy and Commerce Committee, and take the lead on issues like global warming, energy and health care. Dingell is a staunch protector of Detroit automakers, and his battles with Waxman over clean air laws date to the Reagan administration.