The conservative budget-trimming tide has drifted into some unusual nooks and crannies on Capitol Hill this year--even, for example, into the sacrosanct precincts of the Senate's sergeant-at-arms.

Gone from his patronage-prone Senate postal system, for example, are 27 job slots the Democrats had wanted to add before the Republican sweep brought a new crowd into control. Missing, too, are 20 operators for automatic elevators that are not supposed to need operators anyway. And in the Capitol basement there is an old barber shop which, its public subsidy erased, has been consigned to the realm of private enterprise.

These are among the more visible signs of an unusual wave of cost-consciousness that washed over the Capitol in numerous little budget fights this year. On one level, the Congress has as always been kind to itself, voting to give members new tax breaks and at the same time let them earn more outside income. On the other hand, however, for the first time in recent memory committee staffing has been restrained and some ambitious building plans are being postponed.

It is not the year of great austerity that the Republicans had hoped to inaugurate. But it does represent a change from the style of ever-increasing staffs, building projects, and payrolls that Congress adopted in the 1970s.

The participants explain it simply: somehow the idea became rooted that it is not good politics to cut the social programs downtown while adding more of the frills and staff with which Congress comforted itself in the '70s.

"There was this whole atmosphere of economy and cutting back in Washington and we thought that this was a good time," recalled Rep. William L. Dickinson (R-Ala.), a leader in the Republican budget-whacking ranks on the House Administration Committee. "The only way to get at it is through the committee staffs and their expenditures."

Dickinson and his colleagues fell far short of their goal of cutting 10 percent from last year's expenditures but they forced House Democrats to retreat from initial plans for the usual hefty increases.

"Since last year's election, there has been less enthusiasm for more staff," adds a House staff member involved in the budget game. "This year is the first substantial turning point."

But if Congress is keeping the spending lid on itself institutionally, it is not abandoning the impulse to treat its members well in some personal budgetary ways. The search for perks goes on.

Congress voted itself a handsome tax break, repealing the $3,000 annual limit on the amount members can deduct from taxes on their Washington expenses. Some estimates say it could mean up to $13,500 a year for each member.

The Senate expanded its free-mail privilege in a move that will require reimbursing the U.S. Postal Service about $25 million more next year than this year. And while it was being stuffy about staffing, the House voted each member a $4,300 increase for official expenses, $8,000 more for back-home office equipment, and a whopping 65 percent extra for air travel back home--a generous package that Rep. Clarence E. Miller (R-Ohio) called "absolutely unconscionable" at a time when other Americans are being asked to make sacrifices.

Very few heads will roll as a result of the spending restraints voted so far for fiscal 1982. In general, what the Republican-propelled trimming in both houses will do is keep the committee staffs and related congressional agencies at levels of the previous year or at levels modestly raised to afford regular pay increases.

That represents a period of pause in the vast empire-building programs that Congress voted itself in the past decade. Committee staffs grew enormously, select committees sprouted everywhere, and payrolls soared.

Between 1970 and 1980, records show, committee staffs alone grew from about 700 to more than 1,900. "We got to the point where we were adding staffs that seemed to do nothing but call up other staffs on the telephone," said one committee aide. "And we got to the point where there was no other place to stack bodies."

The legislative appropriations bill, according to a staff analysis, lops 83 jobs off the staffing level already authorized for fiscal 1982. The House Appropriations Committee, which largely decides what Congress will spend, sliced away 348 positions from the total number requested by committees and various agencies affiliated with Congress.

All in all, the bill calls for spending about $60 million more--in a budget of $1 billion--than the current budget calls for. The increase is about 5.8 percent which, as a committee document notes, is less than the 8.8 percent allowed in appropriations for the executive branch.

In the Senate, the new Republican majority set out to hold the line by cutting 10 percent across the board from the budget requests left over by the Democrats. Most committees, Senate offices and related agencies went along and the end result is that the Senate will spend about $12 million less than it is doing this year, according to an Appropriations Committee analysis.

Some venerable and protected institutions had the lid clamped on. The architect of the Capitol will get about the same money he had last year, and even the expenses for printing and binding felt the slash. The General Accounting Office got $15.5 million less than it wanted and may have to reduce personnel.

The Senate even agreed to give itself less money for security than its policemen wanted. Howard S. Liebengood, the new sergeant-at-arms, sliced slots for 23 officers off the police requests.