Two Northern Virginia Democrats, one trying to make a political comeback and the other trying to move up the political ladder, are scrambling - along with four Republicans - for the seat being vacated by State Sen. Omer Hirst (D-Fairfax).

The candidate attempting a comeback is Jean Packard, 56, the former chairman of the Fairfax County Board of Supervisors who ousted by Republican Jack Herrity four years ago.

Her bid for her party's Senate nomination is being challenged strongly by two-term Del. Richard Saslaw (D-Fairfax), a young and ambitious incumbent legislator who is counting on his service in Richmond and his party connections to make him the victor in Tuesday's primary election.

While the two Democrats have conducted a quiet and polite campaign for the senate nomination, the four Republicans seeking the GOP nomination for Hirst's seat are locked in a more acerbic contest.

Hirst represented the 35th Senate District, encompassing portions of central and southern Fairfax County, for 16 years and was chairman of Northern Virginia's delegation to the General Assembly.

"I ran against Hirst in 1975, and I came closer to beating him than anyone else," Republican hopeful Robert Murrin said recently. "And how that he's retiring, everybody and his brother has suddenly got [the] guts" to run.

So Murrin, a 54-year-old university staff administrator, is particularly galled to have Republican opponents. He calls one of them, attonery James Tate, " a political opportunist who has run a number of times." The other two GOP candidates, William Whalen and Richard Calvert, are referred to by Murrin as "the other two nice gentlemen."

Tate, 35, abandoned a seat in the House of Delegates several years ago to run for Congress and is considered the frontrunner in the Republican primary. Murrin, however, has been making an unexpectedly close race against Tate, a former federal prosecutor, according to Fairfax politicans who are surprised at the vigor of Murrin's campaign.

But it is the Democratic contest that seems to be attracting the most attention as voters weigh the experience and contributions of Saslaw, a 39-year-old real estate salesman, against those of Packard, a longtime conservationist active in county planning issues.

Saslaw points to his support among many part workers and notes that Packard has been out of office four years. Packard, now a lobbyist on Capitol Hill for several urban counties, thinks she has greater name recognition in the country and recalls that Saslaw came in fourth among five legislators elected to the House in his last two campaigns.

She also notes that her election in November would put a woman in the Senate for the first time in the state's history and prove "you don't have to be one of the boys to be effective in Richmond."

Saslaw, who also ran unsuccessfully in a 1974 Democratic congressional primary, calls taxes and transportation the major concerns of voters in his district these days.

Northern Virginia legislators must continue to "sell the Metro system and the need for it to the General Assembly," Saslaw said. The area is also going to be needing additional funds to improve its heavily traveled secondary roads.

Also, Saslaw said, the assembly should take a more acitve role in watching operations of the State Corporation Commission so that utility rate increases caused by mismanagement are rejected.

Packard's long local government service, she said, has taught her the important impact of Assembly actions on Northern Viriginia. "I can offer a different approach and bring more experience than any candidate of either party," said Packard, who says new residents in the country will be the key to the election's outcome.

About 67,860 persons are registered to vote in the district.

All the voters, Packard said, "are interested in Metro, and they want the state to pick up its fair share of the costs." Residents also want "more local autonomy in land use planning and they want more of their tax dollars coming back to them."

While Saslaw and Packard differ more on approach than on specific issues, the four Republican candidates are more openly divided on the campaign issues they are stressing.

Though Tate outlines a conservative philosophy that includes opposition to the Equal Rights Amendment, abortion the District of Columbia voting rights amendment and collective bargaining for public employes, Murrin questions Tate's commitment on these issues.

Murrin, for example, promises to introduce an antiabortion bill in the assembly if elected, something he said Tate did not do while he was a delegate.

Richard Calvert, 40, a data rprocessing worker, has made perhaps the most interesting campaign promise in the GOP race. He says any group that wants specific legislation introduced need only get a petition signed by 1 percent of the district's registered voters "and I will present that bill regardless of my pesonal feelings."

William Whalen, 34, a self-employed real estate agent, ran for the House of Delegates as an Independent two years ago. He said legislators should spend less time "filling the hopper with bills" and more time being "a go-between for their people."

He won't name names, but Whalen is critical of office-holders who "preach fiscal austerity while they live a life of debt, much as the government does. With the exception of the ERA, which he would "tend to vote against as drafted," Whalen said he "has no hard line on any particular issue." CAPTION: Picture 1, RICHARD SASLAW . . . trying to climb ladder; Picture 2, JEAN PACKARD . . . attempts political comeback