Republician gubernatiorial nominee J. Marshall Coleman came out swinging tonight in a debate televised state-wide, accusing his Democratic opponent, Lt. Gov. Charles S. Robb, of being a "Johnny-come-lately" who lacks the experience to hold the state's job.

Robb countered that it is the equality of leadership rather than years of experience that is paramount, noting that President Reagan, whom Coleman is championing, was elected governor of Calfornia without previous experience in state government.

At the end of the 90-minute forum, broadcast live by the state's five public television stations, supporters of both candidates said they had accomplished what they wanted.

"We struck a difference between them, especially on the tax issue," said Robb manager David Doak.

"We established the difference. There was some confusion about their relative experience," said Coleman manager Anson Franklin.

Most reporters who watched the show in the studio of WCVE rated the debate a toss-up.

The candidates shook hands afterwards and appeared pleased with their own performances. Both then set off for parties at downtown hotels, with Robb's affair serving to celebrate his 42nd birthday.

In his closing statement, Robb alluded to misstatements by Coleman, but said he did not wish to make specific challenges tonight.

"The truth will ultimately prevail," said Robb. He urged voters to "look at what we say, look at the quality of our support and put our statements up to the light of truth. Ultimately, we are talking about leadership."

In his summation, Coleman further allied himself with the Republican administration in Washington, saying that he is "one Virginia son who is ready for the challenge" being espoused in what he called "the Reagan era."

Coleman's reference to himself as a Virginia "son" was part of his not-so-subtle effort to point out that while he was born in the state, his opponent was not.

Robb, who before the first debate at the College of William and Mary was believed to be less oratorically adept than the Republican nominee, pointed out that while Coleman had written his final remarks, Robb spoke extemporaneously.

Robb also chided Coleman about his campaign slogan of "We've got a good thing going" by saying "We need to do more. We need to make a good thing better."

Coleman began the program by saying that while he espoused "creative conservatism," he wasn't sure what Robb's philosophy was except that "he is attempting to shed his Great Society image," a dig at Robb's father-in-law, the late President Lyndon B. Johnson.

Coleman said that Robb has been "remarkably silent on every issue." He asked, "Which is the real Chuck Robb, the one who supports Ronald Reagan this year or the one who supported Jimmy Carter last year?"

Robb responded that the focus of his campaign is on Richmond rather than Washington. He accused Coleman of promulgating "slick, media oriented" issues.

The candidates responded to a series of questions posed by a panel of three reporters.

They sharpened their differences on their approach to taxation.Coleman repeated his pledge to oppose any new or additional taxes while Robb said it is unrealistic to promise in advance to veto any tax package approved by the legislature. Both men said that while they would like to reduce or eliminate the sales tax on food, they wouldn't promise that it would happen during their administration.

Coleman gave whole-hearted support to proposed tax cuts by the Reagan administration, and said the state should cut back on its own taxes. "When Washington is cutting back . . . when Washington is returning responsibility to us, it is no time add new programs in Virginia,"

Robb expressed some reservation about an all-encmpassing block grant approach to federal aid, saying he worried that the "truly needy and disadvantaged" might be "thrown in to compete" with other programs.

But the similarities between the candidates more than outnumbered the differences. Both said they would retain the 55-mile speed limit if that authority is shifted to states, neither would tamper with existing state law that permits abortions in limited instances, both would make education and economic development top priorities and both pledged a get-tough approach on crime.