Former senator Paul Laxalt (R-Nev.), unable to raise enough money to run his campaign, announced yesterday that he is withdrawing from the race for the Republican presidential nomination.

Laxalt, 64, who had portrayed himself as President Reagan's ideological heir and closest friend, said in his statement that he "wasn't about to embark on a campaign that would have led us into a financial black hole."

"We have thoroughly tested the political and financial waters for the past four months," Laxalt said. "While the political response was encouraging, the financial outlook was not as bright."

Laxalt, who was widely considered a long shot and had pegged his hopes on a good showing in the New Hampshire primary in February, issued his withdrawal statement through campaign offices here and in Nevada. He remained at his mountain retreat in Nevada.

Laxalt had not formally announced his campaign, but had indicated he would in September.

When he announced the formation of his exploratory committee on April 28, Laxalt, who had been governor of Nevada and a two-term senator, said he had to raise $2 million by October to run a respectable campaign. The campaign so far has raised only half that, and in the statement, Laxalt said a "careful and realistic assessment of our financial situation" had compelled him to withdraw.

Laxalt said that although a number of fund-raisers were scheduled, he concluded that the $2 million was unobtainable. "We are a family of very modest economic means and I wasn't about to embark on a campaign that would lead us into a financial black hole . . . . The money in my opinion would have been inadequate to conduct a viable presidential campaign."

Political associates and friends of Laxalt said the former senator had been surprised at his difficulty in raising money and was unhappy with the drudgery of the campaign trail. He had been reluctantly drawn into active campaigning in August, including a mid-month New Hampshire swing in which his commitment to the race and his stand on issues were widely questioned.

Republican strategists suggested that Laxalt's withdrawal was unlikely to cause a major ripple in the status of the six other candidates seeking the GOP nomination: Vice President Bush, Senate Minority Leader Robert J. Dole (R-Kan.), Rep. Jack Kemp (R-N.Y.), former Delaware governor Pierre S. (Pete) du Pont IV, television evangelist Marion G. (Pat) Robertson and former secretary of state Alexander M. Haig Jr. Bush, Dole and Robertson also have not yet formally announced.

Republican pollsters and strategists considered Bush the front-runner, with Dole second and Kemp and du Pont battling for third place. Laxalt, along with Haig, appeared to be the longest shot.

"To the extent that his withdrawal has an impact, it probably helps Bush as much as anyone because it throws some Reagan supporters . . . back to Bush, who was their second choice," said Robert Teeter, a leading Republican pollster. "Financial support and political support are related to each other. Fringe candidates get in and hope something will happen and when it doesn't, they have to get out."

Said one consultant, "The most surprising thing about Laxalt's run is that he wasn't even hurting Kemp . . . . I just don't think it will be much of a factor."

When Laxalt announced, Republican strategists predicted he would either hurt Bush, by laying claim to be the candidate closest to Reagan, both personally and on issues, or Kemp, by competing with him for the most conservative Republicans.

Laxalt's withdrawal might prompt some other Republicans to take a second look at the race, according to Doug Bailey, a Republican campaign consultant.

"There's been speculation for a long time as to who the conservative challenger to Bush might be," Bailey said. "There was a flicker about {Sen. Jesse} Helms {R-N.C.} and then {Sen. William} Armstrong {R-Colo.} and then {former White House communications director} Pat Buchanan because a lot of people weren't satisfied with the field. Laxalt was running partly in response to that search. Does this mean that the quest will resume?"

Laxalt had campaigned in about a dozen states and had scheduled a series of fund-raising events in September. But many Republican professionals didn't think that his effort had had much impact.

After Laxalt formed his exploratory committee, he settled a libel suit against the McClatchey newspaper group in California, which had published stories charging that "skimming" of gambling profits had taken place in a casino owned by Laxalt's family. The stories never charged that the Laxalts were involved in the crime.

Laxalt had attracted to his campaign a string of old Reagan political associates and friends, including Gerald Carmen, Reagan's New Hampshire campaign chairman, Reagan pollster Richard Wirthlin, and a string of others. But his campaign staff was regarded as inexperienced.