Conservative fund-raiser Richard A. Viguerie of McLean will formally announce his bid for the Republican nomination for lieutenant governor Tuesday.

Viguerie, a national leader in the use of direct mail to raise millions of dollars for conservative social causes, has been exploring his chances for election since early December. His interest in the job surprised state GOP leaders who said he had never been active in the state party.

Since then, Viguerie has formed a political action committee -- separate from his own organization -- called Campaign for Virginia, which he said will raise $400,000 for conservative Republican candidates running for the 100-member House of Delegates in this fall's legislative elections.

An aide to Viguerie said he will make his announcement in Richmond early tomorrow and then make a traditional campaign swing around the state that will take him to Northern Virginia as well as Norfolk and Roanoke.

He is scheduled to attend a party unity meeting in Richmond today during which candidates for statewide office are expected to promise to limit their criticisms of each other.

One candidate, 8th District Rep. Stan Parris of Fairfax, who is running for the gubernatorial nomination, has said he will not attend; he clashed last week with his opponent, Wyatt B. Durrette, over who was distorting the other's voting record.

Viguerie, who ran for vice president on a conservative third-party ticket in 1976, has drawn criticism from some Virginia Republicans, including former governor John N. Dalton, for being critical of the party.

He also may draw criticism for his stances on defense spending and capital punishment.

Viguerie recently said he has changed his view and no longer supports capital punishment because it is the taking of a human life. Viguerie has been a longtime opponent of abortion for the same reason.

On CBS-TV's "Face the Nation" program yesterday, Viguerie said he supports an across-the-board spending freeze by the federal government, including defense spending, which is a politically sensitive issue in Virginia.

Viguerie dismissed comments that he had been almost as critical of President Reagan as Democrats had been and that Reagan did not think Viguerie represented many conservatives.

"If I were the president, I wouldn't be worried about what Richard Viguerie thinks or says. I would be worried about what his constituents feel, and his constituency out there is very disappointed," Viguerie said.

Viguerie, 51, is considered a wild card in the Republican race that has attracted former state attorney general J. Marshall Coleman, also of McLean and the party's GOP nominee for governor in 1981, Del. A. R. (Pete) Geisen Jr. of Augusta County, State Sen. John H. Chichester of Fredericksburg and Washington lobbyist Maurice Dawkins.

Party officials said Viguerie could use his direct-mail expertise to attract thousands of new participants to the GOP's series of meetings to select delegates to its May 31 convention in Norfolk. The meetings begin next month.