WASHINGTON - Sen. Edward M. Kennedy's diagnosis of a malignant brain tumor has left Congress without its best deal maker and boldest liberal, a politician known for his staunch positions and willingness to work with right-wing lawmakers.

The Senate opened 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 on Wednesday signed a measure that Kennedy forged with Republicans to protect people from losing their jobs or health insurance because their genes say they are prone to future illness.

Whenever there was a deal to be made on important legislation, the scion of the famed political family was somewhere nearby despite his 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 mark on 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.

Conservative Sen. Pat Roberts, R-Kan., added, "Although it is no surprise there are areas where we have a difference of opinion, there are also many areas where we worked together, particularly on child-care and disability issues."

In a climate that often values party loyalty and making political points more than making laws, there is a dearth of potential stand-ins.

Sen. John McCain, the likely GOP presidential nominee, is perhaps the closest. But his alliances with Democrats on campaign finance, immigration, torture and other issues has tested the patience of his party's conservative base.

House Speaker Nancy Pelosi, D-Calif., reached out and negotiated a $168 billion plan of tax rebates and other measure with Bush this year.

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.

Republican Sen. Lindsay Graham of South Carolina has cut deals with Democrats on getting conservative judges confirmed, banning torture in interrogating terrorism suspects, getting tougher with China on trade and expanding health care for members of the National Guard and Reserves.

But none has the reputation and record that Kennedy has in assembling coalitions and keeping them together.

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

While Kennedy is not officially a member of Senate leadership, few deals are struck without his viewpoint being sought. Kennedy is the second-longest serving member and is not up for election again until 2012.

Kennedy's absence leaves a hole in Congress and a definite delay for legislation the powerful Senate Health, Education, Labor and Pensions committee chairman was working on.

Doctors said he will stay at his home over the Memorial Day weekend while awaiting further test results that will help determine his treatment plan.

That means a delay in the personal negotiations he had planned for overhauling higher education, allowing all police, firefighters and other first responders to unionize and strengthening privacy protections in a bill to expand the use of information technology in health care.

Kennedy's not finished, lawmakers said, calling his illness merely a setback. "He's unstoppable," said Sen. John Kerry, D-Mass.