WASHINGTON — Arlen Specter is a senior U.S. senator who expects to be allowed his say on the Senate floor. So he bristled when Sen. Harry Reid, the majority leader, brusquely cut him off at the end of the Iraq debate.

"The leadership is setting a dictatorial tone," Specter, R-Pa., said Thursday, still furious over his treatment the day before. "Senators didn't get here to be pushed around."

It may seem small-minded to bicker over a few words at the end of a 24-hour debate. But the clash between the two veteran senators is evidence of a larger breakdown in relations in the Senate, a deterioration in cooperation that is hobbling the Senate's ability to get things done. The situation is not likely to improve with a presidential election on the horizon.

As the cots were rolled away and lawmakers left for a decent night's rest after the around-the-clock debate that ended — like others this year — in stalemate, lawmakers of both parties said they had rarely seen the tone so poisonous and the willingness to work together on the floor at such a low ebb.

"The last vestiges of courtesy seem to be going out the window," said Sen. Trent Lott, R-Miss., who has served as majority and minority leader during his almost 20 years in the Senate. "Every time I think the Senate — Republican or Democrat — has gone to a point where you can't go any lower, we go lower."

It is hardly startling that members of the two parties do not see eye to eye. And the spirit of bipartisanship in the Senate always rises and falls depending on the subject and the election calendar. But seven months into the new Democratic regime, the environment seems unusually hostile. Occasionally, senators do, too, as exhibited in a Sunday television exchange between Sens. Jim Webb, D-Va., and Lindsey Graham, R-S.C., that looked for a moment as if it might turn physical as the two men argued about the war in Iraq.

Hard feelings have consequences. Without agreements between the leaders of the opposing parties, the Senate has been plunged into a procedural knife fight, with Democrats forced to scramble to find 60 votes not just on contentious issues like an Iraq withdrawal plan, but on once-routine matters like motions to proceed to a spending bill. The feuding has spilled into subjects that would seem to hold the potential for common ground, like antiterror legislation and lobbying reform, and will doubtless tie up spending bills, health care measures and others to come.

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.