Last year Charles G. Viars of Arlington tried to get Virginia Democrats to give him the party's nomination to run against Republican Sen. John W. Warner.

This year Viars is back on the political hustings, but this time he is a Republican and trying to get Warner to speak at a fund raiser for his race against Democratic state Del. Warren G. Stambaugh in southern Arlington's 49th House District. Arlington Democrats say that very few of them had heard of Viars, an executive with an engineering firm in Reston, when he told party leaders in 1982 and in 1984 that he wanted to run against Warner and would glady accept a draft at the state Democratic convention.

Many Republicans in the county also said last week that they knew little about Viars, other than that he had contacted party members to ask them to consider his candidacy against Stambaugh, a 12-year member of the legislature.

What dumbfounds them, several Republicans said, is that the 50-year-old Viars announced at a party meeting last month that Warner would speak at a fund raiser for him a year after Viars gave some Democrats a letter pledging an all-out effort to defeat Warner.

"I was flabbergasted," an Arlington Republican said. "It's just something the likes of which I've never seen in county politics."

A Warner spokesman said the senator, who is mentioned as one of Viars' supporters in Viars' current campaign literature, will not be campaigning for Viars but declined to comment further.

The senator's office is said to have received a copy of the letter that one of Viars' friends circulated among Democrats last year to pitch Viars' candidacy for the Senate, and Warner is said not to be amused by the letter, which is currently making the rounds of both parties.

Viars, a former minister, said in an interview last week that he believed that he had destroyed all copies of the letter, which he said went to only a few Democrats.

"All it was," said Viars, "was a memorandum about a fantastic possibility . . . that Democratic Senate nominee Edie Harrison would not have been nominated, and here was someone else you could consider . . . . I wasn't a fly-by-night individual out to make a name for myself."

The incident, local Republicans said last week, is an example of Viars' naivete, a flaw that could handicap him in his uphill struggle to unseat the 41-year-old Stambaugh, who Viars says is too liberal for his district.

Stambaugh, a lawyer who is the senior Northern Virginia member on the House Finance Committee, says he is taking Viars seriously.

But the Democrat dismisses some of the Republican candidate's charges and positions as "dumb issues" and "examples of his ignorance of what's going on."

Viars has said he wants to introduce a bill to let funeral processions cross municipal boundaries without having to switch to a different police escort at each border.

Stambaugh calls it "not exactly a burning issue with anyone I know."

Viars has said he wants to promote grandparents' visitation rights in divorce cases, a right Stambaugh said is already incorporated in state law.

Viars' platform includes plans to reduce the number of stickers state residents have to pay for and display on their vehicles, and a change in the way real estate is assessed so that recent sales would not influence the value of nearby property.

Said Stambaugh, "I'm running on my record."

It includes, he said, the hard-fought passage of a law guaranteeing certain rights to disabled Virginians, additional funds for the Metro transit system and the county's transportation network, the passage of various tax reform measures and cost-cutting health care bills.

He said he expects that the major issues in the 1986 session will concern state finances in light of expected federal tax law changes and how the state will apportion revenues among competing and critical needs in education, health care, transportation and other state services.

"It sounds like a worn-out song, but clearly financial issues will dominate the next session," said Stambaugh, who also serves on House committees on health, welfare and institutions; labor and commerce, and interstate cooperation.