Arlington County Board member John G. Milliken announced his bid yesterday for the Democratic nomination to challenge 10th District Rep. Frank R. Wolf (R-Va.) in a race expected to be one of the most costly and hard fought in Virginia this year.

With former Virginia governor Charles S. Robb at his side, Milliken launched his campaign before 250 cheering supporters at George C. Marshall High School in Fairfax County, which is expected to be the campaign's major battlefield for votes.

Robb and Milliken, a former chairman of the Arlington board, quickly portrayed Milliken as a Robb-type candidate: a fiscal conservative and a moderate on social issues.

"He can appeal to a broad base of the electorate," said Robb, the popular Democratic former governor who is serving as Milliken's honorary campaign chairman. "He has a commitment to fiscal responsibility, he has a natural base, and he has the experience."

Milliken, 40, a lawyer who is not expected to be challenged for the Democratic nomination, pledged to bring "the special qualities of the Virginia experience to Washington."

"We will offer the voters a choice between Frank Wolf's old-time politics of ducking the issues while the deficits are piling up versus the Virginia experience in governing -- the experience which reduces deficits, fights for priority programs and policies, and invests in the future of our country," he said.

The race is expected to be the toughest for Wolf since he unseated Democratic representative Joseph L. Fisher of Arlington in the 1980 Reagan landslide -- and put Milliken, who was Fisher's top aide, out of a job.

The state Democratic Party has targeted the race as one that Milliken -- whom Robb described as Fisher's "logical heir" -- can win, despite Wolf's advantages as an incumbent who has captured increasing percentages of the vote with each election.

Optimistic Democrats note that, for the first time in 12 years, the congressional race will be the only contest on the ballot in the most populous areas of the district, which covers Arlington, Loudoun and northern Fairfax counties and the cities of Falls Church and Fairfax City.

Although Arlington, a Democratic stronghold, will have other contests, a Wolf-Milliken match would be the only one on the ballot in Fairfax and Loudoun counties, which account for 65 percent of the district's registered voters.

That will require strong efforts by the parties to get out the vote, a task some Republicans say could be hampered by divisiveness in Fairfax County's Republican Party, whose moderates are trying to wrest control from New Right conservatives.

Polls commissioned on Milliken's behalf show a large number of newcomers in the district who are as unfamiliar with Wolf as they are with Milliken. The polls show that those voters view themselves as fiscal conservatives and moderates on social issues on which the Republicans have adopted conservative stances, Milliken backers say.

Wolf "is out of step with the mainstream of thinking" in the district, said Milliken, who expects to raise at least $500,000 for the race.

Milliken supporters say the polls show that although Wolf has a good reputation for constituent services, he is not recognized as having a major role in national or foreign issues."

Citing his experience on the Hill, as a former chairman of the Metro transit board and as a County Board member, Milliken said he has had an equally long record of working on local issues affecting federal workers, education, the environment and area transportation needs.

He charged that Wolf "has dropped the ball" on national issues that affect constituents' lives. "He has either ignored, sidestepped or voted wrong on most of the important issues that we face," Milliken said. "He has become part of the problem in Washington, and he appears to have little interest in looking for a solution."

He accused Wolf of "ducking the tough issues" and cited the incumbent's voting record on the Gramm-Rudman-Hollings balanced budget law as an example. Wolf cosponsored a House version of the Senate bill and then withdrew his support, Milliken said.

Wolf, who could not be reached for comment yesterday, said last week through a spokesman that he is "not surprised" by Milliken's candidacy and intends to run on his record.