WASHINGTON (AP) - Legislation that promises companies billions of dollars in pension relief has sailed through both the House and Senate but is now caught up in a separate dispute - what Democrats say is an assault on their congressional minority rights.

The Senate last week passed a bill that would reduce by $80 billion the money that employers have to pay into their defined benefit pension plans this year and next. The Senate bill also would provide $16 billion in relief over the two years to airlines and others required to make catch-up payments to underfunded plans.

Since the House passed a somewhat different version last fall, commonly the next step would be a House-Senate conference to work out a compromise that both chambers would then approve and send to the president. But Senate Democrats have blocked Senate Majority Leader Bill Frist from naming conferees, protesting what they say is a pattern of being shut out of the negotiating process.

"I have no desire to hold the pension bill," Senate Democratic leader Tom Daschle said this week. "There is an urgency to this legislation, but we will not, on any legislation this year, tolerate the unacceptable experience we had on several occasions in the first session of this Congress."

Daschle was responding to GOP charges that he was obstructing legislation direly needed by companies facing financial ruin because of the high cost of pension plans.

Democrats are particularly angered by two huge bills that House and Senate Republicans wrote last year with little or no input from Democrats.

Only two moderate Senate Democrats, and no House Democrats, took part in lengthy negotiations on the Medicare prescription drug bill that passed, and Democrats said they were completely locked out of talks on the energy bill that eventually failed in the Senate.

Rep. Steny Hoyer of Maryland, the House's second-ranked Democrat, has repeatedly pressed Republicans for what he says is the undermining of the democratic process. "I simply observe that that is shutting out the representatives of 130 million Americans on our side of the aisle to give their perspective."

But House Majority Leader Tom DeLay, R-Texas, in a floor exchange with Hoyer, said Republicans were equally frustrated when they were the minority. He said the process was open to those willing to work with the majority, but "you do not waste a lot of time with people that do not want a bill."

House-Senate conferences, a tradition since the 18th century, have often been a source of contention. During the New Deal, for example, liberal Democrats sought to exclude conservatives, including Democrats, from the list of conferees named by House and Senate leaders.

"It often backfires when either one side or the other perceives a conference as being held unfavorably to them," Senate historian Donald Ritchie said.

That happened last year when the House and Senate both passed an aviation bill that barred the privatization of air traffic controller jobs but Republican conferees, under pressure from the White House, rewrote it to include some shifts to the private sector.

Angry Democrats, joined by some Republicans, forced the bill back into conference and eventually the administration gave ground, agreeing to a one-year moratorium on privatization.

Daschle argued that the pensions bill could still go forward without a conference: The Senate could send its bill to the House, allowing it to either accept the Senate version or further amend it. Or there could be "pre-conferencing," informal talks among staff and members to iron out differences before a formal conference is held.