Democrats threatened Tuesday to slow or stop most Senate business if Republicans unilaterally change the rules to assure confirmation of President Bush's controversial court appointments.

Any such change would mark "an unprecedented abuse of power," Sen. Harry Reid (search), D-Nev., wrote Majority Leader Bill Frist (search), R-Tenn. "The power to confirm judges includes the right to use well-established Senate rules to reject nominees."

Reid, the Democratic leader, exempted military and national security legislation from the threat, and said his rank and file would not block passage of measures needed to ensure continuation of critical government services.

Republicans rebutted swiftly, Frist in the lead. "To shut down the Senate would be irresponsible and partisan. The solution is simple: Return to 200 years of tradition and allow up or down votes on judges," he said in a written statement.

Reid's letter raised the ante in a long-simmering struggle over Bush's court appointments. Democrats blocked votes on 10 nominees out of the 214 sent by the White House during the last Congress, attacking them as too conservative to warrant lifetime appointments.

Accusing Democrats of obstruction, Republicans sought to make an issue of it in the elections last fall, in which they gained four Senate seats.

Bush has already renominated some of the judges, and Reid has said previously the Democrats' position has not changed.

Thus far, Republicans have not sought a Senate vote this year on any of the judicial appointees whose confirmations Democrats blocked in 2003 and 2004.

But under pressure from conservatives, Republicans have floated the possibility they will change the rules that currently allow a filibuster — meaning supporters of a nominee must gain 60 votes to force a final vote. A formal change in Senate rules requires 67 votes, but in this case, the GOP has mapped a strategy requiring a simple majority to make the change.

There are 55 Republicans in the current Senate.

Both parties have made use of the filibuster rules in the past when in the minority. Reid wrote Frist that Republicans, too, would someday lose a majority, and find themselves needing all the rights the minority currently enjoys.

Apart from the exceptions he outlined in his letter, Reid wrote, "we will be reluctant to enter into any consent agreement that facilitates Senate activities, even on routine matters."

The Senate's rules give strong rights to the minority and, in many cases, permit even an individual senator to interfere with the daily routine of committee meetings, floor debate and votes on legislation.

Reid did not specify the steps he is planning to take if Republicans change the rules, but Democrats said he has a variety of options at his disposal.

Reid offered to work with Frist to improve the procedure in which the president makes nominations and the Senate considers them, "consistent with constitutional checks and balances."

He publicized the letter by appearing on the east steps of the Capitol, across the street from the Supreme Court.

Chief Justice William Rehnquist (search) is suffering from thyroid cancer. Democrats and Republicans, anticipating President Bush will have at least one vacancy to fill on the high court, are girding for a monumental confirmation battle.

In his statement, Frist said: "I am committed to getting the work of the American people done in the Senate, which includes advice and consent on the president's judicial nominations as outlined in the Constitution. Never before in the history of the Senate has a nominee with clear majority support been denied an up or down vote on the Senate floor because of a filibuster."

"The Democrats have it backwards," said Sen. Orrin Hatch, R-Utah. "They broke with a long-standing tradition of giving judicial nominations that reach the Senate floor an up or down vote, and we simply want to restore that tradition."

Sen. Arlen Specter, R-Pa., the Judiciary Committee chairman, has declined to express support for a change in the rules but said Reid moved prematurely.

"Since there's no imminent move by the majority leader to move to reduce the filibuster number from 60 to 51, it seemed a little untimely for Senator Reid to make his statement," Specter said. "My focus is to proceed to try to get these judges confirmed and try to work it out, without coming to the confrontation on the constitutional or nuclear option."

Democrats countered that Republicans have long made use of filibusters, circulating a list that said 31 current GOP members of the Senate had voted to block a final confirmation vote on a judge a total of 213 times.