Virginia Gov. John N. Dalton, in a surprise announcement, said today he will not challenge Independent Sen. Harry F. Byrd Jr. in 1982, nor will he seek a job with the Reagan administration when his term expires in January.

"The height of my ambition was to be governor of Virginia," Dalton said. "I've attained what I set out to do and I think it's time to go back into the private sector."

The 49-year-old conservative Republican governor, who is prohibited from succeeding himself after his four-year term ends, said he was making the announcement now to give the state's GOP time to groom others for the Senate race.

While Dalton emphasized that he plans to retire from politics, he added that "no politician is ever likely to say he will never again seek elected office." But he said he is not interested in a federal judgeship and the he already has turned down an unspecified offer to work in the Reagan administration.

"I intend to return to the private sector in a capacity as yet undetermined," Dalton told a news conference, adding he will become either a business executive or a lawyer after he leaves the Governor's Mansion.

Republican politicians, generally stunned by Dalton's statement, groped for explanations. "I am astonished. . . . Such action certainly strengthens Sen. Byrd's hand," said State Sen. Raymond Garland (R-Roanoke).

Garland, a longtime Dalton ally, speculated that his early withdrawal might have been prompted by a secret agreement with the senator. "There may already be an understanding that [Byrd] run as a Republican," Garland said.

Byrd, who left the Democratic Party in 1970 to become the second person elected to the Senate as an independent, declined to comment. An aide said it probably would be months before the white-haired, 66-year-old senator would announce if he will seek a fourth term.

Dalton said today he had urged Byrd to run as a Republican as recently as two weeks ago, but said he had received no indication what the senator would do. The governor refused to speculate whom he would support if Byrd ran as an independent against a Republican candidate.

"Let's cross those bridges as we come to them," said Dalton.

Rep. Paul S. Trible (R-Va.), who was mentioned by Dalton today as a likely GOP Senate nominee, greeted the governor's announcement with elation. The 34-year-old congressman, who represents the Newport News area, said that "if Sen. Byrd retires, I would be interested" in the nomination.

"I believe the party will put forward a candidate in 1982," Trible said, but like Dalton he added, "I would like to see Harry Byrd be that Republican candidate.

Whether to challenge Byrd long has been a devisive issue within the Virginia GOP. After a bitter intraparty struggle, it challenged him in 1970 and lost in a three-way race.

The party's conservatives blocked any GOP nominee against Byrd in 1976, fearing a another three-way race would assure a Democratic victory. Since then Republicans have won repeated victories in the state and some, including Trible, say the party has an obligation to field a candidate for the Senate next year.

Trible said he had no idea who might seek the nomination if Byrd runs again as an independent, noting that "the only two names I've heard mentioned are John Dalton and Paul Trible." But Trible said that "it's no longer a problem for Republicans, as the dominant force in Virginia politics, to find candidates."

Some of Trible's friends expressed doubt that he would be willing to give up what may be the safest seat in Virginia's congressional delegation -- he won a third term last November with 91 percent of the vote -- to challenge a man whose name is synonymous with Virginia politics, and who rolled up the largest vote ever given to a candidate in the Old Dominion in winning a third term five years ago.

Trible said he has $60,000 left over from his easy 1980 race but denied that the surplus is being held as a war chest for a Senate campaign.

While Dalton was discussing his future on the fourth floor of the state Capitol, two floors below the Democratic-controlled State Senate affirmed the governor's political clout by agreeing to strike from its calendar a bill that would have honored slain civil rights leader Martin Luther King Jr. with a state holiday.

Richmond Sen. L. Douglas Wilder, the sponsor of the bill, which Dalton vetoed last week, asked the measure be killed after he conceded he could not muster the two-thirds vote needed to override Dalton. Noting that Virginia honors Confederate generals Robert E. Lee and Stonewall Jackson with a state holiday, Wilder argued that King deserved equal status and said he would try again next year to pass the bill.

The only attempt to defeat a Dalton veto this year failed today when the House fell far short of the necessary two-thirds vote on a bill by Del. Lewis Fickett (D-Fredericksburg) that would have revamped teacher grievance procedures.

Fickett, charging that an amendment proposed by Dalton would turn his bill into a "worthless scrap of paper," had urged his colleagues to reject the amendment and pass the bill. The amendment was rejected by a vote of 60 to 37, but the final vote on the bill gave Fickett only 55 votes, far short of the 66 he needed to overturn Dalton's veto.