Rep. Frank R. Wolf (R-Va.) has been a loyal supporter of President Reagan, but at a GOP luncheon last week with Office of Management and Budget Director James C. Miller, the congressman declared that he would not back the Reagan budget.

"I made it clear to him, as did most of the other members there, that there will be major, major changes," Wolf said after the meeting, which was held for Republicans on the House Appropriations Committee.

Wolf swept into his Northern Virginia seat with President Reagan's election in 1980, and Wolf has twice won reelection as an active and loyal ally of the popular president. This year, however, the conservative congressman has begun to put distance between himself and the president's budget and tax initiatives.

"I have a different approach and a different agenda [than Reagan] on a lot of issues," Wolf said in a recent interview. When asked if he thinks that Reagan's budget is fair, he replied: "In a lot of areas, I don't think it is."

Part of the reason for Wolf's increasingly critical attitude is clear: The White House is making a concerted attack on issues that have concerned Wolf and many Northern Virginia voters, including Metro, student loans and an array of federal employe issues.

Moreover, all this comes in a year when Northern Virginia Republicans and Democrats agree that Wolf could face his toughest Democratic challenger, Arlington County Board member John G. Milliken.

Milliken, who attacked Wolf's ties to Reagan programs in his initial campaign announcement last month, said he does not think the congressman will be successful in disassociating himself from the president.

"He has been such a loyal soldier in the Reagan army," said Milliken. "He can't have it both ways. He can't be a loyal soldier in the Reagan army while disavowing his policies."

Wolf said that he will run on his record and not on Reagan's agenda. He declined to say exactly where his positions differed from Reagan's, except to criticize proposed budget cuts that would affect public employes and Metro.

"I don't have the budget in front of me," he said, sitting in his Capitol Hill office. "There are a lot of issues . . . and as they come before my committee -- I'm on the Appropriations Committee, which is the most powerful committee up here and which makes a determination on each and every one of these issues -- at that time, I'll be making my position clear."

Wolf's 10th Congressional District includes Arlington, northern Fairfax and Loudoun counties and the cities of Fairfax and Falls Church. The area has grown rapidly since Wolf took office, with a substantial immigrant community in Arlington and new subdivisions springing up everywhere from Tysons Corner to Reston and Sterling.

The growth means an influx of new voters without old ties -- voters, Wolf said, who might not be aware of his work, such as his efforts to promote growth at Dulles International Airport.

Unemployment in the 10th District is generally lower than the national average, and incomes generally higher. The area is well educated: More than 40 percent of the people in Fairfax and Arlington are college graduates, and a number work for the federal government, are retired federal employes, or do business with the government.

Wolf appeared to be reserving judgment on some of the Reagan initiatives that have created protests from voters in the area -- proposed cuts in programs such as student loans, mortgage credit and Medicare. But he has been vocal in his opposition to Reagan initiatives affecting federal employes. Reagan wants to raise the federal retirement age from 55 to 62 and to tie a 1987 pay raise to increases in employe retirement contributions.

His concern about federal workers, Wolf said, was one of the reasons he voted against the Gramm-Rudman-Hollings deficit reduction act.

Wolf's votes on the measure have become an early campaign issue, with Milliken dogging him with accusations of flip-flopping on the issue. "His pattern is to duck the issue by voting on both sides," said Milliken.

Wolf was originally listed as a sponsor of the bill, but Wolf said that was an error. "They put it on without my approval."

A week later, he asked that his name be removed, and it was. This sort of mix-up "happens on almost a continual basis," said Wolf. "I am constantly getting my name confused with [Michigan Democrat Rep. Howard E.] Wolpe, and ending up on bills" that Wolf did not cosponsor.

In November, he voted for the Gramm-Rudman bill "to keep the process alive." At that time, House Democrats and Senate Republicans were jousting over the final product. Wolf said he disliked the final product, so he voted against it.

Gramm-Rudman canceled a 3.1 percent raise that government retirees were expecting in January. The law is expected to force federal agencies to cut employment in coming years.

The tax bill pushed by the Reagan administration in December proved to be equally troublesome for Wolf because it proposed eliminating certain tax benefits for public employes. So despite White House pleas for support, Wolf joined a revolt to defeat the rule, blocking the House from considering the bill for a week.

The following week, however, Wolf voted for the rule. He reversed himself after the House leadership agreed to include his amendment to restore the tax benefits for public employes in a GOP tax alternative, which no one expected to pass. Wolf was not allowed to offer his amendment to the tax bill that passed. There was no final vote on the bill.

Wolf nevertheless views that episode as a victory, saying that chances are greater now that the Senate will eliminate the provision. "We won that one," he said.