WASHINGTON - Sen. Edward M. Kennedy's diagnosis of a malignant brain tumor left Congress this week without its best dealmaker as well as its boldest liberal, a politician known simultaneously for his staunch left-wing positions and for his willingness to work with right-wing lawmakers to get legislation passed.

The Senate opened its debate on paying for another year of the Iraq war without the Massachusetts Democrat's customary roar of outrage. Just as evident was his absence when President Bush yesterday signed a law Kennedy forged with Republicans to protect people from losing their jobs or health insurance because their genes say they are prone to future illness.

The president paid tribute to Kennedy at the White House signing ceremony, saying the liberal senator "has worked for over a decade to get this piece of legislation to a president's desk."

Whenever there was a deal to be made on an important piece of legislation, the scion of the famed political family was somewhere nearby despite his celebrity reputation as one of the Senate's last liberal lions.

That willingness to buck his own party and cut deals means that Kennedy has left his stamp on a raft of health care, civil rights, welfare, housing, education, foreign affairs and other issues.

"He has crossed the aisle and sponsored so many legislative enactments," said Sen. Arlen Specter (R., Pa.).

Kennedy yesterday walked out of Massachusetts General Hospital with his wife, Victoria, smiling and waving to onlookers and giving a thumbs-up.

Doctors said that Kennedy, 76, had recovered "remarkably quickly" from a brain biopsy and that he would stay at his home on Cape Cod over the Memorial Day weekend while awaiting further test results that would help determine his treatment plan.

Kennedy's absence leaves a hole in Congress. In a climate that values party loyalty and making political points more than making laws, there is a dearth of potential stand-ins.

Sen. John McCain of Arizona, the presumptive GOP presidential nominee, is perhaps the closest, but his alliances with Democrats on campaign-finance legislation, immigration, torture and other issues have tested the patience of his party's conservative base going into the November election.

Democratic House Speaker Nancy Pelosi reached out and negotiated a $168 billion package of tax rebates and other measures with Bush earlier this year. And Rep. Barney Frank (D., Mass.) has put together bipartisan coalitions for advancing measures to save hundreds of thousands of strapped homeowners from foreclosures and secure civil rights for homosexuals.

But none of them holds anywhere near the reputation and record that Kennedy has in forging interparty coalitions and keeping them together. The list of issues Kennedy has influenced is long and varied.

In 1973, after the Watergate scandal, Kennedy cosponsored an early bipartisan campaign-finance bill. It established new contribution limits and a public-financing provision for presidential elections.

He was instrumental in enacting the Americans With Disabilities Act of 1990, the State Children's Health Insurance Program, and other health-care initiatives. And he was a key Senate backer of Title IX, a 1972 amendment requiring colleges and universities to provide equal funding for men's and women's athletics. He has also been a champion of minimum-wage increases, pushing the most recent effort to raise the minimum wage from $5.15 to $7.25 by 2009.

Standing at his side for many of his legislative accomplishments is usually a Republican whom Kennedy has worked with to get results.

"He remains the single most effective member of the Senate if you want to get results," McCain said.