Democrats contend that Republicans have embarked on a strategy of delay, using Senate rules to chew up scarce legislative time and deny Democrats any accomplishments. Republicans complain that Democrats are trying to jam through objectionable bills and are mainly interested in building a political case for 2008. The relationship between Reid and his Republican counterpart, Sen. Mitch McConnell of Kentucky, has cooled after it was initially thought the two Senate tacticians would be able to do business.

Sen. Edward M. Kennedy, D-Mass., who has been in the Senate for more than four decades, said he was not sure bipartisanship is at an all-time low, but acknowledged that things are tense.

"The fact the Senate is so evenly divided makes big causes out of smaller events," Kennedy said. "My sense is the debate is sharper-edged in terms of the public discussion, and that has reflected to some extent on the institution."

Besides the narrow 51-49 majority Democrats enjoy, lawmakers and others attribute what senators decry as a lack of comity to various reasons, including the emotions surrounding the Iraq war debate, a Republican payback for Democratic stalling in recent years and pure political maneuvering in a hot-house environment.

Reid on Thursday blamed Republican ideology, saying the Senate's conservative contingent was unwilling to swallow legislation sought by most Americans.

"We don't have many moderate Republicans in the Senate," Reid said. "Republicans in the Senate do not represent mainstream Republicans around the country."

Members of both the House and Senate have been contending for years that the sort of personal interaction that can lead lawmakers to overcome partisan differences has been on the decline, leaving Congress polarized.

But Kennedy, Specter and others say they find that committee leaders still tend to be able to work together and, indeed, Kennedy and Sen. Michael B. Enzi, R-Wyo., have cooperated on a major higher education measure the Senate was considering Thursday. And a bipartisan group of senior lawmakers put together the Senate's immigration proposal, though it went down in flames to the broader political divide in Congress.

It is on such big topics that the Senate is stumbling as neither party seems willing to give much ground, locked in a permanent political campaign although Senate terms were made longer than those of the House so that Senators would have a better opportunity to rise a bit above politics.

Sen. Carl Levin of Michigan, the chairman of the Armed Services Committee who has been in the heat of the battle over the Iraq legislation, said he did not believe feelings were frayed beyond repair. After all, Levin said, democracy was built upon the notion of vigorous debate.

"The Senate is a unique place where wills are tested, and this was a very important issue that people have very strong feelings on," Levin said, referring to the Iraq debate. "Instead of fighting over it physically, there are battles that are fought on the floor of the Senate. But these are important disagreements and they should be aired.

"Isn't that what we are here for?"