The Fund for a Conservative Majority, one of the nation's giant, conservative fund-raising organizations, is preparing to spend at least $100,000 in the Virginia gubernatorial campaign this year, believing Republican J. Marshall Coleman's race against Democrat Charles S. Robb will be viewed around the country as a referendum on the Reagan administration and its policies.

"We cannot allow Coleman to lose," says Paul Dietrich, executive director of the fund, who adds that other conservative political action committees (PACs) will be invited to join in an independent, high-budget campaign in Coleman's behalf.

The fund's media-oriented effort, which would be waged in addition to the state GOP's own $2 million campaign for Coleman, could be the first battle in a war among national political organizations of opposing ideological views, fought in the hustings of Virginia.

Whether all of the conservative PACs will go along with the idea is another question. John T. (Terry) Dolan, director of the National Conservative Political Action Committee (NCPAC), the largest of the right-wing fund-raising groups, said yesterday he isn't anxious to help because he isn't convinced Coleman is a conservative.

Dolan said the attitude of some of NCPAC's very large Virginia contributors is "to hell with him.They don't think Coleman is a conservative. Some give him the benefit of the doubt and say he is nothing (ideologically); some think he will cooperate with conservatives, but others think he is an out-and-out liberal."

Dietrich, whose PAC spent $2.1 million last year to help elect Reagan, says he will ask his board next week to approve "an initial expenditure of $100,000 to $200,000" for the Coleman campaign, with "a 50-50- chance" that even more will be available later.

For his part, Coleman says he is "seeking support wherever I can get it." And he adds: "I have no intention to reject it," even though it might subject him to the same criticism his campaign chairman, Gov. John N. Dalton, already has aimed at Robb on the subject of out-of-state campaign financing.

Robb spokesman George Stoddart said yesterday a large gift from Dietrich's group "would obviously hurt us -- $200,000, no matter how you launder it, pays for a lot of 30-second commercials."

But Stoddart contends the effort oculd backfire. Coleman's "association with some of these irresponsible groups could hurt him with Virginia conservatives," he says. "Most people see this campaign as a referendum on Virginia's future. We're not running against Reagan. In fact, we have no problem with what the administration's doing. But Marshall's running a campaign closer to Washington, D.C., than to Richmond, Va."

A White House aide also downplayed the referendum theme. "If you've got two guys down there with no clear differences doing Ronald Reagan imitations, where's the mandate?" said the aide, who asked not to be identified.

Before deciding exactly how to invest its money in the Virginia campaign, Dietrich said his organization will commission a poll "to find out if Coleman is stronger than the ticket." If his running mates, Nathan Miller for lieutenant governor and Wyatt Durrettee for attorney general, are found to have strong appeal, the Fund is likely to buy ads boosting the entire ticket. If not, the campaign will concentrate on Coleman.

"In any event," Dietrich says, "it will be a completely positive campaign. We probably won't even mention Robb."

The Fund is prepared to spend $1.1 million on the Virginia gubernatorial race and on campaigns next year in Ohio, Illinois and Michigan because they are "critical to the 1984 election," according to Dietrich. The Republicans now control all those statehouses.

Based in Rosslyn and formed in 1968, the Fund raises money by direct mail, telephone solicitation and, in the case of large contributors, personal contact. Many of its donors are associated with Young Americans for Freedom, the American Conservative Union and other "old Right" groups. Most of its supporters live in the South and Southwest, Dietrich said.

According to NCPAC's Dolan, Coleman's attempt to make the Virginia election a referendum on Reagan is "smart politics." A recent NCPAC survey, Dolan said, found Reagan has a 71 percent favorable rating in West Virginia. "And he didn't even carry that state," Donal said. "Imagine what Reagan's popularity is in Virginia, where he won big."

Still, Donan believes that "Paul [Dietrich] is viewing [the Virginia race] through the wrong end of the periscope." Coleman's prospects ride on the popularity of Reagan, not the other way around, in Dolan's view.

Anson Franklin, Coleman's campaign manager, says that of the $2 million the campaign expects to raise on its own, "no more than $200,000" will come from out-of-state sources. Of the approximately $700,000 the campaign is believed to have received so far, Franklin said $70,000 has come from the Republican National Committee and the Republican Governors Association, and "probably $15,000 to $20,000" from out-of-state donors whom he declined to identify.

Most of that amount is the result of an April 15 fundraising letter by Dalton, written to out-of-state supporters "to alert you to the first major election that will test the popularity of President Reagan's policies and approach." It warns that if Coleman is defeated, "the politicians will read it as a public repudiation of the President's policies. And the press will write it that way, too." In a handwritten P.S., Dalton noted that under Virginia law, "corporate checks are legal for this race and we have no limits."

In a more recent campaign letter, Dalton wrote that "there are already reports of outside, national, Democratic money flowing into our state in amounts we've never seen or dealt with before." Pressed for specifics at a recent press conference, Dalton said he had heard that Lady Bird Johnson, widow of Lyndon B. Johnson and Robb's mother-in-law, was soliciting funds over the phone from friends in Texas and Oklahoma.

At a press conference Thursday, Robb said "a very insignificant percentage" of the money raised to date, believed to be approaching $900,000, has come from any out-of-state source. The Democratic nominee said he expects to get "a modest amount . . . that certainly would not exceed" 10 to 15 percent of his $2 million budget.

Four years ago, Robb was accused to trying to "buy" an election when he spent a recond $892,000 in winning the office of lieutenant governor. Nearly $123,000 of that came from personal loans Robb made to himself. Much of the rest came from such out-of-state LBJ notables as Averell Harriman, Clark Clifford, Abe Fortas and Mrs. Johnson.