Sen. Patrick J. Leahy (D-Vt.), who has moved into a position of local power in Washington as chairman of the Senate District Appropriations Subcommittee, is developing a reputation for political unorthodoxy.

As a member of a party often criticized for free-spending policies. Leahy has been ranked by the American Taxpayers Union as one of the Senate's 12 most fiscally conservative members.

As a member of a body that usually begins committee hearings at 10 a.m. and goes into session at noon, he sometimes convenes committee hearings at 8 a.m., when witnesses seem barely awake.

Among colleagues who often complain that they need more staff assistance or who thirst for more patronage, Leahy has deliberately budgeted only $442,000 of the $588,000 legally available to him for office operations. He returned the other $146,000 to the Treasury.

During the summer congressional recess that ends Wednesday, Leahy broke with another tradition of Congress.

Instead of maintaining office operations in Washington on a business-almost-as-usual basis, as do most law-makers Leahy virtually closed shop and sent 12 staffers to Vermont for face-to-face contacts with constituents usually dealt with by telephone or mail.

Only a few people were left behind, chiefly to answer the telephone and administer a summer intern program.

For Leahy, what has come to be known as "the projuet" was born of a growing belief that lawmakers, their families and their office staffs tend after a while to think of themselves increasingly as Washingtonians and less as residents of their home states.

Both the government and the backhome constituents suffer as this happens, Leahy said in an interview here. Government tends to become something for "insiders" rather than truly representative, he contended.

Leahy, who was prosecuting attorney of Chittenden County (Burlington) when he was elected at age 34 in 1974 to succeed retiring Sen. George D. Aiken, spends about 40 weekends a year in Vermont tending chiefly to political chores.

Staff members who returned for the summer were instructed to shun politics, said Paul A. Bruhn, Leahy's administrative assistant.

"I know this sounds trite," Bruhn added, "but I never felt that there has been much difference between good government and good politics."

All but two of Leahy's staff members were recruited in Vermont, but most never had met constituents they began dealing with by mail or telephone from the capital.

So last month, Liam Murphy, who ordinarily handles agriculture problems in the Washington office, worked on a farm in Addison County.

Margaret Gross, who monitors federal fund-grant grograms, visited recipients and potential recipients. Other staffers similarly traveled to meet people involved in their fields of specialization.

One overcast morning last week, Gross slogged up a mountainside lumber-hauling road near Waterbury to inspect a woodlot where otherwise useless trees were being felled and ground into chips for use as heating fuel at a nearby state hospital.

If the experimental state-funded project proves successful, Leahy may be called to help obtain funding for more widespread adoption of the woodburning solution to national energy problems.

This is important to Vermont, where 75 per cent of the land is covered by forests, many of them comprising otherwise economically useless second growth.

Leahy's position on the Appropriations Committee could then be of strategic importance to Vermont. His District Appropriations chairmanship definitely is not.

Leahy said he was confronted recently by one constituent who, with interest and not rancor, noted that the authorized $300 million federal payment to the District of Columbia is several times as large as Vermont's total budget.

Vermont's population is about 450,000, slightly more than half that of the District. Its largest city, Burlington, has 40,000 residents, with another 62,000 residing in the surrounding county.

Interviewed while driving from Burlington to his modest mountainside home. an old farm house 38 miles away in Middlesex, Leahy said the Vermont constituent's comments on the District budget reflect the intense issue orientation of people from rural states.

"Members of Congress spend too much time in Washington and in session," Leahy said. "Certainly it is not a boondoggle to go home or to have staff members go home. You can just be there (in Washington) too much.

"I can't help but feel the country would be better served if we closed down entirely in July and August."

Leahy said he also has personal reasons for wanting Congress to rearrange its sessions.

"In Congress, we are getting more and more young people, like myself. I'm 37, and I was 34 when I was elected. It would give us a chance to be a little more like a real family," Leahy said.

Leahy and his wife, Camille, have three young children. In the Washington area, they live in McLean where the children attend public schools.

A tall, rangy man who is prematurely balding, Leahy has lost more than 50 pounds in the past year. His offices, in Burlington and in Washington, are conducted with informality. The senator is "Patrick" to the entire staff, from receptionist to administrative assistant.

"We never refer to him as "the senator as they do in all the other Senate offices on Capitol Hill," one staffer said.

In Washington, Leahy ordinarily arrives at work about 6:30 a.m. to read mail and documents and dictate letters by tape machine. He said he reads every letter from Vermont and every that deals with a District matter.

Leahy, a Vermont native and son of a retired printer, has strong personal ties to Washington. He attended Georgetown University Law School and often refers fondly to his years there.

That background has helped in his District appropriations chairmanship, Leahy said. That job could consume all of his work time, but other assignments prevent that. He spends part of each day on the chore and regularly confers with Mike Hall, his staff aide on District matters.

"If it's my responsibility to be chairman, I'm not going to do a sloppy job," Leahy said.

Leahy has yet to pass upon a District budget but will do so soon. The House version will be enacted soon.

Leahy said he has no intention of keeping the chairmanship for an extented period, as has his House counterpart, Rep. William H. Natcher (dKy.) for 16 years.

"There is no way I could justify to myself or to the people of Vermont spending year after year as chairman of that subcommittee," he said.

Leahy was reluctant to comment in detail on his observations about the District government, since the city's home rule system restricts Congress' role in its operations.

But he said there is no excuse for inferior education or other public services, given the city's $1 billion annual budget.

Leahy created a considerable stir among District officials by releasing a Library of Congress report last May that showed Washington had the highest per capital cost of government of any American city and by expressing strong reservations about the city's plan to build a convention center downtown at a cost of $120 million.

The city's request for funds to start acquiring land now is pending before Leahy's subcommittee. He said he has instructed his staff to prepare detailed briefing books giving the best arguments for and against the project.

Leahy's decision to bring the staff members home for the summer recess has won widespread praise from Vermont newspapers and officials involved in the project.

One press critic, Proctor H. Page Jr., wrote in the Surburban List, a weekly in the Burlington suburb of Essex Junction, that Leahy's project had a "high fertilizer content."

The Burlington Free Press, the state's largest newspaper, saw it differently.

"While Leahy's idea is astute politically. Vermonters will benefit in many ways from the relationships his aides make while they are here," the paper commented editorially. "And it certainly beats spending the hot, muggy month of August in Washington."