When Republican Frank R. Wolf swept into Congress on Ronald Reagan's coattails in the 1980 election, he probably didn't realize just how difficult it would be balancing his loyalty to the new administration with the wishes of his Northern Virginia constituents.

Last year, despite campaign promises to back twice-a-year cost-of-living adjustments for federal retirees, Wolf voted for a budget that provided for annual increases. Last August, he made what he termed the hardest decision of his two years in the House, rebuffing intense White House pressure by opposing Reagan's tax bill.

"Things are not as black and white as I once thought," said Wolf, 43, a former lawyer-lobbyist from Vienna who is running against Arlington Democrat Ira M. Lechner. A 48-year-old labor lawyer and former Virginia state legislator, Lechner charges that Wolf's loyalty to Reagan has resulted in a record of "broken promises and broken dreams" particularly for the 40 percent of his constituents who are active or retired government workers.

Unlike the congressional race in the neighboring 8th District, where the slashing verbal styles of Democrat Herbert E. Harris II and GOP Rep. Stanford E. Parris have become the dominant theme, the main issue in the 10th District race is Wolf's record.

"I'm very proud of my record and that is the main issue in this race," he said recently. "I've worked extremely hard in a bipartisan manner and I've been very effective."

Lechner calls Wolf's record "reprehensible," a claim with which leaders of federal employe unions--many of which are backing Lechner -- agree. "Frank Wolf is like the arsonist who starts a fire and then calls the fire department," charges Betsy Reid of the American Federation of Government Employees, the largest federal workers union. "He says he's against all kinds of Reagan policies but then he turns around and votes for them."

Wolf says he is an independent-minded Republican who has broken with the administration on several key issues. As evidence, he points to his support for extension of the Voting Rights Act and his opposition to Reagan's tax bill.

"We have attempted to bring people together," said Wolf. "I haven't divided my party or my district." In that vein, he points to his work on relieving congestion at National Airport.

What has proved controversial are Wolf's votes on several issues. Among them:

* Wolf says he did "everything humanly possible to protect semiannual COLA," cost-of-living-adjustments for 23,000 district residents who receive federal pensions. However, he voted for the 1981 budget that replaces them with annual increases, a vote Lechner repeatedly criticizes. He also voted against a proposal called the Bolling Rule that would have provided a recorded vote on COLA and other controversial budget questions. And he failed to stand in support of a motion on the House floor that would have permitted reconsideration of semiannual COLA.("I was prepared to stand but the whole thing happened so fast there just wasn't time," Wolf said.)

"I supported the overall budget, which was a vote on many issues," said Wolf, who voted against the Bolling Rule because "I thought it was a Democratic attempt to dismantle the Republican budget . . . that would not have protected COLA."

* Last May, Wolf voted for a budget proposal sponsored by Rep. John H. Rousselot (R-Calif.) that would have denied Social Security recipients and federal workers and retirees 1983 pay and cost-of-living increases. That was a "symbolic vote" for a balanced budget proposal that had no chance of passing, Wolf said, "and I strongly support a balanced budget."

* Wolf says he led the fight in Congress to remove the pay cap on top-level civil servants. Lechner says the Democrats, not Wolf, were the real leaders. Staff members for Maryland Democratic Reps. Michael D. Barnes and Steny Hoyer contend that their bosses and Parris all fought hard to remove the cap. They said Wolf originally tried to have the cap removal tacked onto an appropriations bill that Reagan announced he would veto, a strategy the Democrats reportedly headed off because they feared it would backfire.

"Frank was sort of like a bull in a china shop," said Barnes aide Matt Pincus. "He just plunged in without knowing what he was doing and he certainly was not the leader."

"That's just not true," Wolf replied. "Steny got it in the Democratic budget and I got it in the Republican and it passed."

* On Oct. 5, 1981, Wolf broke with the administration and the Virginia congressional delegation and supported the extension of the Voting Rights Act. "I took a lot of heat for that," he said, "but I believe in voting rights for everybody. That was not one of my more difficult votes."

Wolf says he is proudest of his work persuading Congress to pass a new administration policy for National Airport. Lechner says the policy is inadequate because it caps the number of passengers at 16 million per year -- 2 million more than currently use it -- and fails to provide sufficiently strict noise standards.

"Everybody patted me on the head and laughed when I said I was going to do something about National Airport," recalled Wolf, who says the Carter administration proposal called for an even higher passenger cap of 17 million. "I did it as a freshman and a member of the minority."

Wolf has sponsored 10 bills, three of which have passed. One is a resolution designating National Construction Industry Week, another designates National Newspaper Carrier Day and a third provides for rebuilding Wolf Trap's fire-destroyed Filene Center.

On many social issues Wolf sides with the New Right, a fact Lechner often mentions, citing Wolf's 1980 support by the Moral Majority and a recent campaign contribution from an organization headed by Paul Weyrich, an architect of the New Right. Wolf opposes the Equal Rights Amendment, which Lechner cosponsored in the Virginia House of Delegates. He favors a constitutional amendment mandating voluntary prayer in the public schools and another banning abortions except in cases where the mother's life is endangered, both of which Lechner opposes.

Wolf said he agonized most over his vote against the tax bill, which provides for a politically painful tax increase in an election year. "The bill had a lot of good features," said Wolf, who opposed its elimination of tax-exempt industrial development bonds.

"A lot of congressmen and cabinet officers live in my district," said Wolf, who turned down a coveted invitation to Camp David before the vote because he didn't think it was "appropriate to eat the president's food and pretend to be undecided." Treasury Secretary Donald Regan, one of several Reagan surrogates who have campaigned for Wolf, dropped by his office to try and change his mind.

"Being a freshman minority member of Congress in this economic environment, I think I've done an excellent job," Wolf said. "And I think if the voters look at the record, they'll see that."