The lights were up. Spectators filled the galleries. Legislative clerks stood at the ready. Binders with the day's legislation -- a $54 billion spending cut -- were on the leaders' tables.

There was only one thing missing from the House chamber yesterday: lawmakers.

On either end of the Capitol, insurgents brought the legislative process to a halt, forcing GOP leaders in the House and Senate to shelve prized tax and spending cuts. The explosions went off almost simultaneously, as if they had been synchronized -- and authorities blamed both attacks on Republican moderates.

After five years of relative quiescence, centrist Republicans in both chambers chose yesterday to make a stand. At the Senate Finance Committee, Olympia J. Snowe (R-Maine) forced Republican leaders to cancel a committee vote on a $60 billion tax cut. In the House, a rebellion by a few GOP moderates shut down the chamber for nearly six hours and led leaders to abandon a vote on budget cuts.

The Senate panel's hearing was scheduled to start at 10 a.m., but at 11 lobbyists and reporters were milling around in the hall outside the nearly empty hearing room. In another room, GOP panel members, with Majority Leader Bill Frist (Tenn.), struggled to salvage the legislation.

Sen. Rick Santorum (R-Pa.), a conservative, emerged from the closed-door meeting to have his photo taken, smiling, with constituents. "We'll know in a few minutes," he said. More than a few minutes later, he emerged again, no longer smiling. "We're still working," he announced.

Finally, at 11:35, an aide emerged, telling lobbyists and reporters to go home. "The markup is being postponed until a call of the chair," he said in parliamentary lingo, "and that's not likely to be today."

The cause of the trouble, Snowe, emerged moments later, chased by a pack of reporters. She cut an unlikely figure for an insurgent: The slight and soft-spoken senator explained that a tax cut of this sort is not "what we should be doing now." Stepping onto an elevator to escape the pack, she pointed out that "we've had three back-to-back hurricanes."

Sen. Kay Bailey Hutchison (Tex.), part of the GOP leadership, walked past the committee room and heard what had happened. "I'm very concerned," she allowed.

Over on the south side of the Capitol, the House television network, which broadcasts the chamber's proceedings, instead displayed a photograph of the Capitol grounds in summertime and a message: "The House is in recess subject to the call of the chair."

There were signs of trouble the night before, when House leaders sent out the day's schedule with a notice saying, "Last votes expected: unknown."

While the chamber was immobilized and GOP leaders pleaded for votes, the moderate Republican Main Street Partnership gathered at the Capitol City Club to claim responsibility for the chaos. The group, often ignored, was not quite ready for the crush of reporters: There were problems with the microphone, and the group's banner was draped clumsily over a bookcase.

The ringleader, Rep. Charles Bass (R-N.H.), acknowledged that "sometimes we can't even agree what day of the week it is." But not this time. "We will not waver," he promised. Rep. Wayne T. Gilchrest (R-Md.) seconded the defiance. "We will hold the line on this," he vowed. "I think this is the dawning of a new day."

Moderates were raging. Rep. Vernon Ehlers (R-Mich.) took the microphone. "They know very well what our position is, and it won't change," he said of party leaders.

Back at the Capitol, the Republican leaders were still predicting passage of the budget cuts by day's end. "I haven't been told otherwise," a leadership spokesman said.

That was at 3 p.m. By 3:30, he had been told otherwise: Republican leaders called an impromptu news conference outside House Speaker J. Dennis Hastert's office.

Majority Leader Roy Blunt (R-Mo.) played quality-control manager. "The product we had today wasn't quite where we needed to be," he said. Besides, he added, "West Coast members have to make planes."

Joining them but saying not a word was Rep. Tom DeLay (R-Tex.), who once maintained lockstep discipline in the House but was returned to the backbenches by an indictment.

Democrats, all smiles and backslaps, held their own news conference in the House television gallery, where they announced that the Republican Party had, officially, cracked up. "Republicans have a massive failure on their hands," said Minority Leader Nancy Pelosi (Calif.). "A failure today of the Republican leadership," said Minority Whip Steny H. Hoyer (Md.).

Only Rep. John M. Spratt Jr. (D-S.C.) gave some credit to the "brave" GOP moderates.

Out on the newly reopened House floor, Hoyer made some mischief at Blunt's expense, asking the Republican leader in a colloquy about the fate of the budget bill.

"We hoped to have that bill on the floor today," Blunt said, tightly. He had better luck passing the next item on the agenda: H.R. 1953, the San Francisco Old Mint Commemorative Coin Act.