Marshall Coleman stands in the shade of a magnolia tree, an image of comfort and suburban ease. Outfitted in a V-neck sweater and button-down Oxford shirt, he easily could be mistaken for a tennis pro discussing the proper backhand with an attentive class.

But when he speaks, he says precisely what the Republican candidate for governor of Virginia had been expected to say. He talks about traditions, about managing money with care, and most of all, about how America, by electing President Reagan, finally has discovered "the Virginia Way."

This is the Marshall Coleman the voters of Virginia will discover this afternoon if they happen to be watching the Tournament of Champions tennis match televised on ABC. The political advertisement -- 30 seconds of time in which the attorney general basks in the wholesomeness of middle-class Richmonders -- heralds the opening of what promises to be the most expensive media campaign for the office of governor in the state's history.

For Coleman, this opening, month-long blitz of commercials crafted by the blue-chip Republican consulting firm of Bailey, Deardourff and Associates, will cost $250,000 -- less than a quarter of the sum he is expected to spend before the November election. His Democratic opponent, Lt. Gov. Charles S. Robb, will counter with a like amount. In the Virginia governor's race of 1981, television is the name of the game, and Coleman has made the first move.

The Coleman that Virginians will see on television starting today is a candidate unafraid of his youthful, 38-year-old looks, comfortable wearing chinos and Top-Siders while talking about budgets, crime and tradition. He will be introduced by a rich-voiced announcer as a "fiscal conservative who worked hard to elect John Dalton and Ronald Reagan."

"You know," the television viewers will hear Coleman intone in a homey twang, "under Jimmy Carter I was the only attorney general who argued against more federal spending for handouts for our offices. And now that President Reagan is in office and has adopted the Virginia Way, I think he deserves a governor who will support him, and that's exactly what I intend to do."

What the viewers will not see are any signs of Marshall Coleman the old "Mountain Republican," the once-liberal-leaning legislator who moved to the left of his state party on many social and civil rights issues. That Coleman now is being presented as the party's conservative heir comes as no surprise to the opposition.

"Their strategy," said George Stoddart, press spokesman for Robb, "is to hide his liberal past and put him in the wraps of his new fiscal conservatism." h

Coleman's first commercial was filmed in Richmond's Byrd Park, a name synonymous with the conservative wing of the state's Republican party, some of whose ranking figures, including former Gov. Mills Godwin, have thus far declined to endorse the Coleman candidacy. But Coleman's advisers insist that the ads are not aimed at such reluctant conservatives. The sole purpose of the commercials, they say, is to help Coleman catch up with Robb in that magical political virtue known as name recognition.

"Robb has glamor status and he's had it for a number of years," explained Coleman's consultant, Doug Bailey. "The ads are intended to solve the only problem we've got -- name identification. So we're going early."

The three Coleman ads that hit the airwaves this week begin identically. Against a blue background, the names of both candidates appear. "One of these two men will be Virginia's next governor," says the ammouncer in a most serious tone. "Here are some things you should know about Marshall Coleman."

One of those things, the ads claim, is that Marshall Coleman was brought up fighting all the odds. "His father died when he was nine," the announcer explains. "He's had to work for everything he's gotten." That work, the ads note, included combat as a Marine in Viet Nam.

For one of the three ads -- the one in Byrd Park -- Bailey asked Coleman's campaign office to recruit a small group of friends, not necessarily true believers, to listen to him under the magnolia tree. The stand about somewhat woodenly, appearing ambivalent, at best, about their candidate and what he is saying. The ad is so sober, in fact, that Robb's people think they can do better.

Two other Coleman ads were filmed with a construction crew in Newport News, where viewers at last will see a black Virginian interacting with the candidate. The message in this ad is hard-line: "I've got a simple theory about fighting crime in Virginia," Coleman is heard telling the hardhats. "When a criminal goes to jail, he serves his full term without any parole."

It is a theory that Coleman has been unable to make a reality as the state's leading prosecutor.