Former Virginia Gov. Linwood Holton, the Republican whom Democratic campaign officials want least to run against in next year's U.S. Senate race, today announced that he is a candidate for his party's nomination.

Holton is one of four Republicans expected to seek the seat being vacated by the retirement of Republican William L. Scott. At four press conferences throughout the state, Holton said he will base his appeal for delegate votes at the party convention June 3 on the claim that he is more electable than any of his opponents.

"The main issue [at the convention] will be electability," he said. "My accomplishments in office, the friendly attitude that Virginians showed toward me when I was governor and since I left office and the most recent polls show that I am well ahead on the electability issue."

Six Democrats already are seeking their party's nomination, also to be decided at a June convention. In interviews at a Democratic meeting here Dec. 10, campaign officials and supporters of these candidates all rated Holton as the strongest opponent the Republicans could field in November.

They said they feared Holton's proven ability to cut into traditional Democratic strength among labor union members and black voters and would prefer to run against former GOP state chairman Richard D. Obenshain.

Obenshain, perceived as more conservative than Holton, led conservative forces against him in intraparty battles in the early 1970s. Obenshain starts the contest for convention delegates with a wide following among city and county chairmen and other party regulars.

State Sen. Nathan H. Miller from the Shenandoah Vally is the third announced GOP candidate and former Navy Secretary John Warner is expected to join the race.

In 1969, Holton took advantage of a divided Democratic Party to become the state's first Republican governor since 1886. He ran then, as he had in 1965, as a moderate, campaigning on the progressive principles of the "Mountain Valley Republicans" of western Virginia.

In answer to questions at his Richmond news conference today, Holton took positions on national issues that were so decidedly conservative that they seemed calculated to make sure that the only issue left between him and Obenshain is electability.

To specific questions, he said he opposes ratification of the proposed Panama Canal treaty, generally opposes use of taxes and direct government controls in dealing with energy shortages, would not approve of using U.S. funds to pay for elective abortions for Medicaid patients and is against extension of the seven-year period now permitted for ratification of the proposed Equal Rights Amendment (ERA) to the U.S. Constitution.

On ERA, which would make discrimination between the sexes unconstitutional, Holton said, "I have always been on record for the amendment, but I don't favor extending the ratification period. I think that might raise a serious constitutional problem."

Asked to predict how his voting record in the Senate would compare with that of Virginia's two conservative senators now in office, Scott and Independent Harry F. Byrd Jr., Holton said:

"You would not find me voting differently from them. Our basic approach is for a private, free economy, for individual . . . ability to choose and make decisions."

Holton, 54, said that a "competitive, two-party system in the Congress is the only way to put the brakes on the federal government." Referring to the overwhelming Democratic majority in Congress, he said. "There is no effective control on the majority now. They have set up a series of fieldoms up there that is taking the power away from the states to Washington."

As a political campaigner in the 1960s, Holton stressed his party's long opposition to the racial segregation policies of the state's old Democratic establishment. During his first year as governor in 1970, when Richmond's school for the first time were operated under a court-ordered busing plan to achieve racial balance, Holton became a symbol of racial moderation in the South by escorting his children to the first day of classes in predominantly black public schools.

In an interview today, he said of that episode, "I have always been opposed to forced busing and still am. But we did that as an act of leadership, to set an example in the hope we could avoid the kind of opposition to busing orders that has occurred in other places, like Boston."

On current U.S. civil rights issues, Holton said he opposes writing affirmative action plans into laws because of the tendency to interpret them as quotas. He said that as governor he persuaded the U.S. Department of Health, Education and Welfare not to try to impose minority enrollment quotas on Virginia colleges. He said he still opposes the "enrollment goals" that HEW is trying to set in Virginia "if those goals can be fairly interpreted as quotas."

As governor, Holton promoted unification and expansion of Virginia's seaport facilities at Hampton Roads, launched sewage treatment improvements statewide, and through appointees brought about conspicuous management changes in the state's voter records office and automobile licensing agency.

Nevertheless, his critics characterized him as an uneven executive handicapped by a lack of knowledge of state government and given to tempestuous dealing with his top advisers. In a soon to be published book on U.S. governors, state government scholar Larry Sabato, a Virginia, ranks Holton as "outstanding," but said in a recent interview that he gave him that rating only because of his success in handling racial matters.

Holton is spoken of approvingly by his followers and derisively by his critics as the "fun governor." He himself says he loved the public functions, including the parties, that are part of the governor's life. He acknowledged in an interview that he probably spent more time in the state airplane than any other Virginia executive and made frequent use of the state yacht and governor's cottage at Virginia Beach.

Of his flight in the state plane to watch Virginia's Secretariat win the Kentucky Derby, Holton said with a mock expression of duty, "I considered it my official obligation."

Of the many amenities furnished a governor, Holton said, "they are provided for the convenience of the governor, and when I found it convenient, I used them."

After Holton left the governor's office in 1974, he served as assistant secretary of state for congressional affairs and then became a partner in the Washington law firm of Hogan and Hartson. He said he will continue to be a member of the firm un. He said he will continue to be a member of the firm until just before the Republican convention.