They were cheering and clapping, elated over Northern Virginia's big financial wins in this year's General Assembly.

"Hail Mary, full of grace; here we are in first place," sang out one member of the Northern Virginia delegation as its members gathered around a huge conference table Monday for their final weekly caucus of the 1985 session.

There was much to celebrate: Northern Virginia will receive more state highway money than ever before. And if counties still aren't satisfied, they have the authority for the first time to spend an unlimited amount of local money on roads. They won money for Dulles International Airport and more for the community colleges. The list goes on and on.

"We had some luck; everything broke right," said Sen. Clive L. DuVal II (D-Fairfax), the senior member of the delegation.

But other voices rose above the claps and congratulations.

"Don't gloat," warned Sen. Joseph V. Gartlan Jr. (D-Fairfax).

"Watch what you say," cautioned Sen. Richard L. Saslaw, a Fairfax Democrat.

Just a few days earlier, Northern Virginia lawmakers were chided on the Senate floor for gloating over their good financial luck.

It all began with one Fairfax delegate's candid assessment of how Northern Virginia fared in this year's budget.

"We made out like bandits," Del. Robert E. Harris (R-Fairfax) had said earlier in the session. That remark enraged Sen. Daniel W. Bird, a Southwestern Virginia Democrat whose mountain district will lose money under the changes in the state road formula that will give Northern Virginia more money.

"We read what they say," Bird said. "They say: 'We're making out like bandits! We're taking home the bacon!' The rest of us get the crumbs."

His admonition left Northern Virginia senators red-faced.

In the eyes of many rural legislators, if there's one thing worse than Northern Virginia beating them on money matters, it's having the suburban legislators brag about it.

Del. Gwendalyn F. Cody (R-Fairfax) suggested: "Say it quietly."

"Just go home with the money," DuVal added.

Northern Virginia legislators are particularly sensitive about their images now. Although they scored a major victory on their hard-fought battle for highway money, they have been warned that many of this year's supporters may turn against them next year on another crucial issue -- funding for the Metro system.

"I anticipate we're going to have a very difficult time next year," DuVal cautioned his colleagues.

Rural legislators led two assaults on the Metro system this year during debates over the new road money formula. The 40-member Senate came within four votes of taking away the $21 million subsidy the state gives to Metro each year.

Sen. Edward E. Willey (D-Richmond), chairman of the Senate Finance Committee, sided with Northern Virginia on the Metro battle this year because he said he viewed it as an attempt to sabotage the delicately drafted roads bill.

"But wait until next year," he told a reporter after one Senate debate. Willey has made no secret of his opposition to the state's contribution to the Metro system.

In an attempt to head off next year's assault, DuVal appointed a committee to begin gearing up for the 1986 Metro budget war within days of the end of the current legislative session.

He directed the team to work the computers with local government officials to "show the revenues we contribute to this state to counter charges that we're double-dipping on Metro and roads."