Virginia Attorney General J. Marshall Coleman, breaking with his state's subdued political tradition, took the offensive in announcing his Republican candidacy for governor today, accusing his Democratic opponent, Lt. Gov. Charles S. Robb, of sidestepping many state issues.

Although Coleman's announcement had long been anticipated, he surprised some by calling for weekly debates with Robb will in advance of the November elections and defied the unwritten dictum that Virginia candidates not even mention their opponents' names. Coleman, who is unopposed for his party's nomination for governor, went further than that, attacking "Chuck Robb" for what Republicans believe to be his major weakness -- his alleged fuzziness on the issues.

"I don't know where he stands on various isues . . . ," Coleman told a Northern Virginia press conference at which he repeatedly chided Robb for supporting Jimmy Carter and sought to tie himself to President Reagan. Coleman said that while he has made more than 2,000 decisions as Virginia's top legal official and as a legislator, Robb's three years in office were marked by a paucity of public positions on state issues.

Although breaking with one Virginia tradition, Coleman wrapped himself in several others, including what he called "the centuries-old Virginia tradition of excellence in public service, and the 12-year Virginia tradition of stable Republican government."

He sung the praises of both the president -- "Ronald Reagan is doing a great job for America" -- and Virginia Gov. John N. Dalton -- "Governor, you have kept us on a steady course." And Dalton, coleman's most powerful political ally, made it clear that he viewed the November election as a referendum on the success of his administration.

"We are completely compatible," Dalton said of himself and Coleman. "If you like what you've seen the past three years and three months, then it's time to go to work." Dalton is ineligible to succeed himself.

Acknowledging the importance of capturing the independent suburban voters who have come to dominate Virginia politics, Coleman kicked off the day at an early-morning rally at the Tysons Corner Marriott in Fairfax County.

Both there, and at a noontime rally before 400 chanting loyalists at the John Marshall Hotel here, Coleman's followers both cheered and laughed at the debate challenge, apparently confident the glib, 38-year-old Coleman would beat Robb, 41, in one-on-one appearances.

An aide to Robb, who kicks his campaign Thursday, responded to Coleman's challenge, saying "Chuck is very much looking foward to having joint appearances with the attorney general." But the spokesman added that the traditional time for such debates is after Labor Day. "As a practical matter," said the Robb spokesman, Charles Fitzpatrick, "we're not sure we'd be able to meet once a week, and we're not sure Coleman was serious about that."

A top Coleman strategist insisted, however, that the debate challenge was deliberate. "You don't run a campaign on the defensive," said Coleman adviser William A. Royall. Royall said Coleman would continue to press Robb for face-to-face confrontations throughout the coming seven-month campaign. "We're going to try to find out where Chuck Robb stands," Royall said.

The Coleman campaign displayed some of the Virginia GOP's top prize winners today, including six of the state's nine Republican congressman, Dalton, and former governor Linwood Holton, who began the GOP's string of three successive gubernatorial victories in 1969.

But the appearance of unity was hurt by the absence of former two-time, Democrat-turned-Republican, governor Mills E. Godwin, whose support is considered critical to wooing conservatives identified with the old Byrd machine, which dominated state politics for two generations.

Coleman said at a press conference at Tysons that Godwin "is, as usual, his own man," but added: "We are keeping in touch and he has been encouraging."

Reached at his home in Suffolk, Godwin said, "I have told both candidates that I am not going to make any comment right now." Asked if it were correct to say that he had been "encouraging" Coleman, Godwin again said "No comment."

But some of Godwin's Main Street Richmond financial supporters were on hand today, indicating that Coleman should have a good portion of the Virginia business establishment that has accounted for much of the GOP's money in recent years.

As was Dalton, Coleman was a relative and somewhat reluctant latecomer to Ronald Regan's bandwagon last year, holding back until late March. He was anything but reluctant in invoking Reagan's presidency today in distinguishing his candidacy from Robb's. "It's no time to change in Richmond when our common sense has reached Washington," he said to the day's biggest cheers.

"You can't have it both ways," Coleman added. "You can't be for Jimmy Carter in June and November and then change your stripes in March."

Coleman also portrayed Robb as vague on issues, in contrast with "the more than 2,000 decisions" he made as attorney general and thousands of votes he cast during six years in the legislature. "He hasn't had an opportunity" to vote, having never served as a legislator, Coleman said of Robb.

But Coleman refused to be pinned down on what issues he would like to know Robb's views on, and skipped over several of his own positions that are not likely to endear himself to many in the right, including favoring the Equal Rights Amendmend and limiting funding for abortions. His positions on both those issues are the same as Robb's.

Coleman also was silent on whether he would support repeal of Virginia's controversial sales tax on food, a perinnial gubernatorial campaign issue, although he did say that tax-cut promises during the campaign would be "premature and irresponsible."

While "we should not be afraid to change," Coleman said to cheers, "many things should not be changed." Among them he listed support of the state's right-to-work law, which conservatives believe is a cornerstone of attracting new industry, and opposition to collective bargaining for public employes, a position on which Coleman acknowledges that he switched after one term in the legislature. Robb's positions on both issues are identical.

Coleman corned his party's nomination in large part by spending three years working the GOP's picnic and chicken-dinner circuit. At both rallies today he displayed the easy confidence that has made him a formidable campaigner. During several pauses for applause here, he winked at supporters standing nearby, who cheered on cue and waved placards that bore photographs of the candidate in the identical pinstriped suit, striped tie and broad grin he wore today.

Two of the three men vying for the Republican nomination for lieutenant governor, state Sen. Herbert H. Bateman of Newport News and former delegate Guy O. Farley of Warrenton sat side by side in the front row here. dThe third aspirant, state Sen. Nathan H. Miller of Bridgewater, was absent today for what he said were business reasons.

Coleman insists that he is neutral in the race, despite suspicions that both he and Dalton much prefer Bateman over Farley because of the latte's born-again Christian stance, which might give some wavering Byrd Democrats and independents an excuse to support Robb.

The only Republican attorney general candidate, Wyatt Durrette of Fairfax, whom Coleman beat for the GOP nomination four years ago, was on hand to introduce Coleman today. The lieutenant governor race is the lone nomination to be decided at the party's state convention in Virginia Beach on June 5-6.

Northern Virginia's new Repulbican Reps. Stanford E. Parris of the 8th District and Frank Wolf of the 10th, agreed that the election will be close.

"Chuck is a very attractive candidate," said Parris, sipping coffee before the 8 a.m. announcement at Tysons. Parris said Coleman will have to "tiptoe through some tricky minefields. If Marshall gets the Main Street money, and the conservative-to-moderate Democrats, that's where the difference will be."

Wolf said that "because both will spend a lot and both are very capable, organization will be the difference."