Richard A. Viguerie, whose direct-mail firm in suburban Washington has raised millions for national conservative causes, today plunged into state politics, announcing he would seek the Republican nomination for lieutenant governor of Virginia.

Viguerie, making his first bid for office in the state, cast himself as an outsider who will "penetrate the buddy system that so often thwarts the popular will . . . . " He has not been active in Virginia politics and some of the GOP's state leaders had hoped he could be dissuaded from entering the contest.

A native of Texas and longtime resident of Northern Virginia, Viguerie, 51, dismissed those complaints today and said his candidacy will attract "tens of thousands of people" to the Virginia Republican Party.

He said he will use some of the direct-mail techniques that have made him famous to attract those newcomers to mass meetings this spring across the state. Those meetings will select delegates to the party's nominating convention May 31 in Norfolk.

Viguerie's potential to generate that kind of support and his blunt, outspoken style, often critical of President Reagan, has unsettled some Republican party regulars. His critics, including former Gov. John N. Dalton, view his campaign as a wild card in a contest that already had attracted four candidates.

His opponents are former state attorney general J. Marshall Coleman, a neighbor in McLean, state Sen. John H. Chichester of Fredericksburg, Del. A.R. "Pete" Geisen of Augusta County and Maurice Dawkins, a Washington consultant. Coleman, a Washington lawyer and candidate for governor in 1981, is considered the front-runner and all the others, except Dawkins, are considered party regulars.

Although Virginia's lieutenant governor is a part-time office holder whose chief responsibility is presiding over the state Senate, Viguerie said it was "a proper place for me to start."

Viguerie's race is expected to provide a forum for some of the state's conservatives and Christian fundamentalists who have been unsuccessful in previous attempts to play a major role in the party politics of a state that tends to elect moderate conservatives.

In an apparent attempt to downplay his national focus, Viguerie today pledged to raise all of his money from Virginia sources. He also listed several endorsements from Northern Virginia conservatives as well as national figures and offered his views on a range of state issues.

He said the state should refund most of its $238 million surplus to the taxpayers, place a constitutional limit on state spending, submit any future tax increase to the voters and allow elections for school boards.

"I am running because I believe Virginia cannot afford four years of confusion . . . of spending gone wild . . . of an inability to perform even a simple function like locking a jail door," Viguerie said in a speech delivered here, in Norfolk and Roanoke and at Tysons Corner.

Some Republicans have faulted Viguerie for attempting to run for vice president as an independent in 1976 and his involvement last year in the defeat of Sen. Charles H. Percy (R-Ill.).

"I have never criticized the Virginia Republican Party," Viguerie said in response to a reporter's question about his GOP credentials.

He claimed credit for playing "an important role" in Dalton's 1977 election as governor as well as conducting "independent campaigns" for other Virginia candidates.

"I'm surprised at that," said Richard Cullen, an attorney and close associate of Dalton's. "I've never heard Gov. Dalton mention Viguerie until the past few weeks . . . ."

Northern Virginia backers listed by Viguerie include Ben K. Partin, chairman of the Fairfax Republican Party, and Guy Farley of Warrenton, a leader of some of Northern Virginia's conservative Christians and a former GOP candidate.

Viguerie's nearly two pages of national endorsements listed the support of conservative Republican Sens. Orrin G. Hatch of Utah, Jesse Helms of North Carolina and Jeremiah Denton of Alabama.