Ronald Reagan's Virginia campaign has won the endorsement of former governor Mills E. Godwin, a conservative power whose blessing should assure Reagan of winning most of the state's 51 delegates, according to state GOP leaders.

Godwin's decision to help lure conservative Democrats and independents to the Reagan cause may make moot the question of support from Virginia's two other top Republicans, Gov. John N. Dalton and Sen. John W. Warner, party officials said.

Godwin, a Democrat-turned-Republican, had been an enthusiastic supporter of John Connally before Connally dropped from the presidential race. This week's switch by Godwin, who squired Connally around at last summer's state GOP convention, cheered Reagan backers.

"We're expecting to take a tremendous majority of the delegates," said Robert Hansenfluck, executive director of the Virginia Reagan for President Committee.

The party already has begun the process of selecting delegates to congressional district caucuses and the state convention. Winners in those contests will attend the Republican National Convention in Detroit in mid-July.

In a state where Reagan overwhelmed the incumbent president, Gerald Ford, four years ago, most GOP officials now view Reagan's chances as being even better.

That assessment is shared to some degree by party moderates who would prefer to see George Bush or others win the nomination.

"Things are not going as well as they might be," acknowledged Del. James H. Dillard II (R-Fairfax), a strong Bush supporter. "Four weeks ago, things were looking really rosy, but you know what's happened since."

Despite Bush's poor showing behind Reagan in recent primary contests, Dillard and other Bush enthusiasts say their candidate will make a good showing in the selection of delegates, especially in Northern Virginia.

Bush supporters recently outpolled Reagan's in Alexandria, and Bush was expected to do well at mass meetings held in Fairfax County last night.

"He's very well-liked here," Dillard said.

Even Republican officials who remain uncommitted, however, say Reagan will run strongly everywhere in the state.

"It's perfectly obvious Ronald Reagan will receive even stronger support from Virginia Republicans than four years ago when we went overwhelmingly for him at the national convention," predicted state Sen. Wiley F. Mitchell (R-Alexandria).

Mitchell, who was pushing the candidacy of Sen. Howard Baker (R-Tenn.) until the latter dropped out of the presidential race, said the big Reagan following "results not so much from affection for Reagan but from a total disaffection for Jimmy Carter or anyone else the Democrats would nominate."

Besides, Mitchell said, the expectation that Reagan will ultimately win the party's nomination has muted some of the criticism and antipathy leveled at him in 1976.

The conservative "Virginia for Reagan" coalition that Godwin is helping to organize will provide a third force that has become something of a state tradition in presidential elections since the early 1970s.

Godwin, the only Virginian ever elected governor first as a Democrat and then as a Republican, has joined before with staunch conservatives and independents to help elect both Dalton and Warner.

The Republican governor, the Republican senator and Republican Attorney General J. Marshall Coleman have declined so far to endorse any presidential candidate.

Dalton and Warner even issued a joint statement earlier this month "declining for the present to declare a preference."

Warner, according to spokesman William Kling, wants to stay above the nomination battle so that he will be free to act as a unifier in case of any bitter party disputes at the state or national convention.

Kling yesterday challenged assertions by Virginia Democrats that President Carter's impressive 6-to-1 showing at party meetings last Saturday will mean a Democratic victory in the fall.

"If Jimmy Carter were running against Scoop Jackson [Sen. Henry Jackson of Washington] or one of the more moderate Democrats and came away with the same kind of landslide, I'd call that a show of real strength in the state," Kling said. "But against Teddy Kennedy? I'm surprised Kennedy got as many as he got."