The brass spittoon still sits near the well of the Senate chamber, not far from the snuff box by the door. Portraits of departed chairmen still grace House committee room walls. But behind the comforting reminders of enduring congressional folkways, the foundation of power throughout Washington -- is being strained dramatically in the early days of the Reagan adminstration.

Not long ago the chairmen of congressional committees and subcommittees were looked upon as almost feudal figures, fearsome protectors of the baronies they helped create with the aid of powerful allies on the outside and formidable traditions within. Even presidents defied them at their peril. Reforms stormed the citadels and came away with bruises as trophies.

The committee chairmen were in business to preserve and, if possible, to expand their worlds. It would have been unthinkable for them to relinquish to others to power to hack away at the borders of their domains.

And yet this is what appears to be happening as Congress now responds to President Reagan's call for program cuts of previously unheard-of size to achieve the budget savings he wants as part of his economic program.

With scarcely a protest, Congress is preparing an all-in-one, fast-track treatment for Reagan's package of cuts that relegates the old barons to the role of kibitzers, adjusters and enforcers.

There is no single reason for what appears to be happening, but rather a confluence of forces that could produce a sea change in the way politics is played and power is wielded at both ends of Pennsylvania Avenue. If only temporary, or only part of an on-going evolution, it is nonethless worth watching.

Most obvious among the reasons is the dominance of fiscal conservatism, including a relentless zeal for budget-cutting, in both the White House and The Congress for the first time in a quarter-century. It was been building for some time, but is now almost holy writ.

Reagan not only has a Republican Senate but also a House that may be only nominally Democratic when it comes to preserving the legacy of many Democratic social programs.

Fearful that Reagan speaks for most Americans in demanding a leaner federal establishment, even many of the dwinding band of Democratic liberals are reluctant to be cast in the role of obstructionists in standing against the retrenchment tide.

But the job of Reagan and the congressional conservatives would be a lot tougher, maybe even impossible, without a handy little tool for short-circuiting the normal legislative process that the Democrats crafted in a far different era, ironically to curb the fiscal powers of another Republican president.

This is the tool called "reconciliation" that Congress, under pressure from the Reagan administration and from its own political imperatives, apparently will use to package and expedite Reagan's proposal for $41.4 billion in spending cuts for fiscal 1982.

It enables Congress to reconcile its budget goals and actual spending practices by forcing its committees to cut programs within their legislative jurisdication. Based on recommendations of its Budget committees, Congress issues lump-sum savings instructions to its committee.

The committees are given a specific deadline for producing the required savings, if necessary by cutting programs that are already in place and fully funded. The cuts can be temporary or permanent. Permenent cuts are planned for this year.

The device was included in the 1974 Budget Control Act as part of a broad effort by Congress to strengthen its control over the federal budget, power that had been eroded by President Nixon's practice of impounding funds that Congress appropriated. In exchange for taking away the president's impoundment powers, Congress set up its machinery for controlling expenditures.

"Reconciliation" was included in this machinery, but it only gathered dust until last year when, in another ironic use, it was revived by a Democratic-controlled Congress, with the support of a Democratic president, in a futile attempt to produce a balanced budget. The result was $8.2 billion off the top of the fiscal 1981 deficit, achieved through both spending cuts and tax increases.

It was a reflection of the already dwinding power of congressional committee chairmen that the "reconciliation" language got into the budget act in the first place. It was an even more telling commentary when it finally came to be used.

In the House last year, the chairmen tried to stop "reconciliation," only to be stampeded by their juniors, who already sensed that their survival hinged more on pursuing austerity than on bowing to rank.

Under "reconciliation," authorizing committees in the House and Senate Budget committees before the Budget committees recommend lump-sum savings that are to be made.

They can also decide how to apportion the cuts within programs falling under their jurisdiction. And they can argue their case on the floor of each house.

But this is a far cry from the power they once wielded on the front lines of an expanding federal establishment, when they were the principal creaters of expansion, not the hapless expeditors of contraction.

If David A. Stockman, Reagan's budget director, and some Senate Republicans had had their way, the contribution of the committees would have been even less than is currently comtemplated. A House Democratic source said they wanted the whole package to be assembled by the Budget committees, even to the extent of deciding the precise program cuts. House Budget Committee Chairman James R. Jones (D-Okla.) reportedly balked.

It isn't just the committee barons who lose under this new procedure. In the Senate, for instance, the power of the minority -- the Democratic liberals for a change -- is sharply reduced by the fact that "reconciliation" imposses time limits on debate and bans filibusters.

The fast-track nature of the process also enables the sponsors of a spending cut package to capitalize on momentum and catch opponents before they can fully mobilize. Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) for instance, wants the Senate to complete action on the spending cut instructions within a month. Even House leaders are talking about completing the spending cut orders by May 15, with the July 4 recess as a target for wrapping up the whole package. m

"This is an extraordinary proposal," said Baker about the packaging and expediting of the spending cuts, "but these are extraordinary times." The price for balking, he suggested, will be paid at the polls in the elections next year.

All of this has the effect of increasing the power of the president, at least when a congressional majority perceives that he has the public behind him and the will go over Congress' head, if necessary, to sir up public pressure for his program. In the case of Reagan, many Democrats concede this is the case.

But, in the view of some House Democrats, it also strengthens the hand of the Democratic leadership in forging a cohesive spending policy for the party in Congress, at least to the extent that the House Budget Committee reflects the views of the leadership, as it apparently does now.

In both houses, the "reconciliation" procedure puts enormous power in the hands of the two budget panels, neither of which existed when most of the program to be cut were created.

Although Jones and his Senate Republican counterpart, Sen. Pete V. Domenici (R-N.M.), have announced plans to push ahead with a "reconciliation" package, the committee and subcommittee chairmen have been noticeably quiet.

"It may not last, but they just seem to have rolled over," said a House aide. He and other attributed the reaction, or lack of it, partly to the fact that Reagan's program and the fast-track legislative agenda for handling it are only a few days old.

But even more important, they said, is the reluctance of critics to be appear as obstructionists. A freguent subject of conversation on Capitol Hill Friday was a full-page newspaper advertisement by the Lone Star Cement Co. that carried the message, "Want to Get Reelected? Don't Pull This Nation Apart . . . Your Voters Are Watching."

Another reason, one aide said, is that "reconciliation," much as the chairmen may not like it, makes it easier for them to make the cuts that their members are demanding.

"It's always easier," the aide noted, "to say the devil made me do it."