Northern Virginia voters were approving a proposal to legalize pari-mutuel gambling at race tracks in the state, according to early returns.

Voters in Northern Virginia, one of the areas mentioned as a possible site for a race track, were supporting the measure by healthy margins in Fairfax and Prince William counties, with narrower margins in Arlington and Loundoun counties.

A second referendum would have to be held in any locality before a race track could be built there.

Opposition to the betting issue was led by religious organizations arguing that gambling is immoral and will draw increasing elements of organized crime to Virginia. Consequently, groups such as the Roman Catholic Diocese of Richmond, the United Methodist Church, the Women's Christian Temperance Union most Baptists fought the issue through a Richmond coalition called Virginians Opposing Pari-mutuel Gambling Inc.

Supporters of pari-mutuel betting, operating through Virginians for Horse Racing included the state Chamber of Commerce, the Virginia State Travel Council, most horse breeders and array of public figures including Gov. John N. Dalton. Their arguments were largely based in the mean 13,000 jobs and bring $25 million a year into the state. Fears of organized crime and moral questions about gambling were not relevant the proponents said.

By last week, however, the proracing group's war chest appeared to have peaked at about $117,000 but horse breeder John D. Marsh of Prince William County expressed concern that the opponents would outspent his group.

The foes of betting had picked up an ally in former Gov. Mills E. Godwin, for the first time, made a formal statement against pari-mutuel betting the Religious Herald news magazine, joining the ranks of the anti-racing crusade.

Other opponents argued that wagering could defile the image of Virginia as state whose values are different from other states. "This is an insult to Virginia's integrity and record of sound government," replied State Del. Raymond R. Guest, a Front Royal Republican and leader in the fight for race track wagering.

Efforts to legalize pari-mutuel betting have had a rough time in Virginia in recent years. Bills to get the question before the public as a referendum failed in the legislature in 1972, 1974 and 1976, although Virginians had overwhelmingly voted in 1970 to strike a provision from the state Constitution that had barred gambling entirely.

Even this year, it took a second vote in the House of Delegates in February before the bill to approve the referendum passed. There was no such trouble in the State Senate.

Under terms of the legislation, approving the referendum, which Dalton signed in April, the state would be limited to two race tracks, and local jurisdictions would have to hold their referendums to approve a track locally. A state commission that studied the issue found Northern Virginia and the Norfolk area as the most suitable sites.

A poll released Oct. 22 by the Richmond Times-Dispatch showed that 48 percent of those questioned favored pari-mutuel betting, while 39 percent were opposed.