These aren't the happiest of days for Northern Virginia Congressman Stan Parris and some other Virginia Republicans.

"We just don't all get together anymore," Parris said, complaining that the solidly conservative Virginia congressional delegation of the past two years is no more. "We were generally ideologically similar in our point of view and therefore more comfortable discussing issues."

The three reasons the delegation is no longer a big happy family are Democratic Reps. Frederick C. Boucher, James R. Olin and Norman Sisisky. They hail, respectively, from Virginia's once staunchly Republican 9th, 6th and 4th districts in the western and Southside areas of the state.

Because of their elections last November, the three Democratic lawmakers are trotted out as "draws" at Washington gatherings. They have been welcomed with surprise and open arms by the House leadership, and are being touted by their party as bona fide celebrities in a state once considered useless to the Democrats' national agenda.

Their arrival in Washington cracked the state's Republican-dominated delegation, which had the reputation of the being the most conservative state delegation on Capitol Hill. And the biggest surprise to many was that the new Democrats--and progressive Democrats at that--weren't from Northern Virginia, where close elections and upsets are the norm.

"Who'd have guessed the changes would be there?" asked a GOP aide, noting that the Democratic victories came in downstate Virginia.

Although Parris and other Republicans complain that the Democrats' arrival has hurt the delegation's clout, the Democratic House leadership says it is encouraged about the state's political possibilities. "The three of them are very supportive of the party, and their election helps out the whole delegation," says Rep. Tony Coelho (D-Calif.), chairman of the Democratic Congressional Campaign Committee. "With Democratic Gov. Charles S. Robb, it makes Virginia a very doable state now."

Republicans say, however, that Virginia remains conservative and that it's too soon to conclude that the state's political complexion has been changed. "I don't think it repesents a trend," says Rep. G. William Whitehurst, the state's senior GOP congressman. "Anybody can get knocked off in any given election."

In the last session, the 10 House members from Virginia, including conservative Rep. Dan Daniel, the only Democrat, often seemed as one. Now there is more opposition in the delegation to many of President Reagan's economic and social proposals. Boucher and Olin are cosponsors of the nuclear weapons freeze resolution--something that would have been unthinkable in what was once a decidedly promilitary group.

"In the past the delegation has had a rather homogeneous hue, and a lot of these issues didn't get a public hearing in the state," says Boucher, who upset Rep. William C. Wampler, dean of the state's delegation and an 18-year GOP veteran. "Now Virginians will get to hear both sides."

Parris says the delegation is back to the place it was between 1974 and 1980 when Democrats Herbert E. Harris and Joseph Fisher represented Northern Virginia's 8th and 10th districts and frequently voted at odds with the rest of the state's congressmen.

"We're going to have votes of 8-2 or 7-3 by and large, which is what used to happen with Fisher and Harris," says Parris, who recaptured his old seat from Harris during the Reagan landslide that also helped Rep. Frank R. Wolf defeat Fisher.

Another disquieting note to Virginia Republicans has been talk of a growing rivalry between the state's two Republican senators, John W. Warner, elected in 1978, and Paul S. Trible Jr., elected in November to replace retiring independent Harry F. Byrd Jr.

Whereas Byrd had no offices outside Washington and seldom went on swings through the state, Trible's hard-charging activism has been more than a match for Warner. Trible has opened more offices in the state than Warner, hosts a weekly radio show and has organized his own Tidewater version of Warner's "Atoka Country Supper."

Some suggest the junior senator is trying to upstage the senior one, but both men are clearly peeved at such speculation. Warner says he and Trible are working as "equal partners" and that he encouraged Trible to hold the Tidewater gathering and intends to participate in it. Trible says he and Warner are working well together "in spite of all those folks out there waiting to see us fall out."

The schisms in the House, however, are quite real.

Boucher, a former state senator from Abingdon, and Olin, a retired General Electric executive from Roanoke, stunned many when they came out in support of the nuclear freeze resolution. Some said such a stance wouldn't play well back home, but the two congressmen say their mail has been running in favor of their position.

Boucher thinks the Reagan view against the resolution has been the view of Virginians in the past "simply because there was no one at home to explain the issue." Olin puts it more bluntly: People in his district, he says, are worried "that somebody's going to start shooting off these nuclear bombs some day."

Their pro-freeze support was attacked by the conservative Richmond Times-Dispatch, which accused the two congressmen of making Soviet premier Yuri Andropov "very happy." The moderate Roanoke Times & World-News supported the men in an editorial headlined "Bully for Olin and Boucher."

Expect the delegation to become "more pro-active rather than reactive," says a key state political aide. As if to prove that characterization, the four House freshmen, including Republican Herbert H. Bateman from Newport News, have plunged into committee work, often carving out interests ignored by their predecessors.

Boucher and Bateman, who worked together in the legislature, have joined the Science and Technology Committee, where they hope to encourage the development of new industries. Boucher has become the first Virginian to serve on the Education and Labor Committee, where he wants to improve training in mathematics and science. Olin, surprisingly, is the only Virginian on the Agriculture Committee, where he looks out for the interests of his farming constituents. Bateman has a seat on the Merchant Marine and Fisheries Committee, also important to his Tidewater district.

Sisisky landed a coveted spot the Armed Services Committee, where two other Virginians already serve and where he says he was privy to information that persuaded him to oppose the freeze resolution. The millionaire soda pop distributor and former state delegate from Petersburg is also, along with Olin, on the Small Business Committee.

While the new Democrats had Robb put in a good word for them with the House leadership during committee assignments, some of the Repubicans were less pleased with where they landed. Some have suggested that Whitehurst--the Virginia Beach Republican who cochairs the delegation along with 8-term Democrat Daniel--didn't do enough "horse-trading" or that Whitehurst just didn't have enough to horse-trade with after the elections.

"This business is a business of leverage, and when we lost votes, we lost influence," says Parris.

Whitehurst minimizes the disputes, admonishing that "squaring off at the drop of a hat for political reasons is not the Virginia way." And, he notes: "It's not so partisan that we don't speak to each other. We all won our own elections, and we cooperate."