Virginia Lt. Gov. Charles S. Robb was asked recently if rumors were true that he had loosened up his Marine Corps-every-hair-in-place image since taking office last Janurary.

"I don't think so," said Robb, a Democrat who is the first Northern Virginian in decades to hold statewide office. "I think it's just that people are getting used to me."

Indeed, if the people of Virginia aren't used to Chuck Robb by now, they soon will be. The 39-year-old lawyer, with family money and investments to support him, has given up his practice with a Washington law firm and made the part-time lieutenant governorship a full-time job.

Many consider him the Democratic Party's best chance for capturing the Republican-held statehouse in 1981 and for reversing what has become a string of Democratic defeats statewide in Virginia.

With the apparent defeat of Democratic senatorial candidate Andrew P. Miller waiting to be confirmed today by the state Board of Elections, Lt. Gov. Robb is the only Democrat in the last eight years to be elected to a statewide office. Democrats still hold a large majority of the seats in the General Assembly, but have failed in several attempts to elect candidates for governor and senator.

Robb, generally believed to be the only statewide figure acceptable to all philosophical factions of the party, is, in short, its chief hope. And so, the man who barely two years ago was described wryly by former lieutenant governor Henry E. Howell as having "parachuted in here" is being looked to increasingly as the one to pull the party through this latest setback and lead it to future victory.

"I think Chuck is looked upon as the titular head of the Democratic Party," said Senate Majority Leader Adelard L. Brault (D-Fairfax), who praised Bobb for his "all-out effort" in campaigning for Miller and said Democrats in the state would remember his hard work.

"The people of Virginia have gotten to know him and they like him." Brault said. "I think he's going to be our next governor."

Chuck Robb is often described as so straight you could use him to draw a line. He doesn't drink coffee; he drinks milk. His entire career from high school onward has been marked with such achievements as "student commander of all Army, Navy and Air Force ROTC units on campus . . . ranked first in company and first in entire class in leadship . . . received Seven Society Award . . . Bronze Star with Combat V . . . "

Married to the former Lynda Bird Johnson, daughter of the late president, Robb has had easy access to Johnson era political strategists and his mother-in-law, Lady Bird Johnson's own campaign contacts. But he downplays the importance of his Johnson family connections in his political success, saying his mother-in-law's role "was probably played out of proportion" during his campaign a year ago. "Most of her time she spent baby-sitting with the children."

Robb at this point is appropriately coy about his ambitions for the governoship, while making no secret of his interest, is life for the present, is near future is a combination of official speeches and appearances in all parts of the state (and occasionally out of it) and an increasingly important role in meanding and building the state party.

He is, however, reluctant to talk about his work in revamping a weak and underfinanced party organization.

"It was clearly import to us to win the race," said Robb, who discussed the recent Warner-Miller Senate electin in an interview last Friday at his office in Fairfax City.

He says he and Republican John Warner, the apparent winner, "are good close, personal friends," but he regarded Miller as "superbly qualified for the job" and expected the contest between them to be "more of a party election" than one based on personalities.

"In than respect," Robb said, Miller's apparent defeat "was a major disappointment" that could adversely affect the Democratic Party "if we let it bet the best of us."

But Robb refused to involve himself in what he sees as "witch hunting and finger pointing" against some individuals who have been blamed for the party's failures, such as party chairman Joseph T. Fitzpatrick and members of the central committee who have controlled the state party since 1972.

"It's more important to worry about where we go from here," said Robb, who stressed he had never sought a role in the party's leadership "per se" but has been thrust into a leadership position "because of the way the election (in 1977) worked out."

The Virginia Democratic Party, in Robb's view, in the past has wrongly focused on individuals instead of the party organization. He credits the Republicans, particularly the late Richard D. Obenshain, with doing a better job of consolidating and increasing their political power while Democrats continue to feud over differences in idology.

In an effort to build the "strong, viable party organization" he says is essential to Democratic election successes, Robb has formed a Democratic Advisory Committee to study the way things are done in other state organizations and present a report.

Robb freely acknowledges that a well-organized party is also essential to any political future he might have. "Of course," he said recently, "I have a vested interest."

The advisory committee, a small group chosen to represent the party's various philosophical and geographic interests, is chaired by former Sen. William B. Spong. Party chairman Fitzpatrick is a member but has not attended any meetings and just last week criticized Spong and Robb for mailing out a questionnaire to party officials soliciting detailed critiques of the Miller campaign.

The lieutenant governor's only required duty is to preside over the Senate during the one or two months a year the legislature is in session, but Robb says the post "has clearly evolved into essentially a seven-day-a-week job requiring all my time and attention, almost to the exclusion of my wife and family . . . who are very understanding."

The job pays $16,000 a year in salary and $5,000 in expenses, although last year Robb persuaded the legislature to give him a budget of about $113,396, out of which he pays for a staff of five and office expenses.

Previous lieutenant governors, including Robb's Republican predecessor, Gov. John N. Dalton, operated out of cramped offices in the state Capitol and their hometown offices with a staff of volunteers or people paid out of the officeholder's personal funds or by political backers.

As the only Democratic member of the state's excutive branch, Robb had difficulty finding appropriate headquarters in Richmond but finally located himself in the historic three-story Bell Tower on the Capitol grounds.

Built in 1824 and more recently used to store fertilizer and grounds keeping equipment, Robb's choice of an office was initially satirized in newspaper cartoons. But he has settled comfortably into these quarters, says he gets good exercise climbing the 3 1/2 flights of stairs of his top floor office and even uses a Bell Tower symbol on his stationery.

Robb said the Republicans "gave me a hard time" about the increased budget and his office expansion. "But I told them I understood because it'll be the last thing they'll ever be able to get me on."

Besides, Robb said, his professional staff is paid poorly and rarely reimbursed for such expenses as driving from Northern Virginia to Richmond. Although he expects much of his own money to be contributed toward the office's operations, he said he will not know much until the end of the year.

"Because I'm the only Democrat holding statewide office or because of my campaign or people's perception of me," Robb said, his office is inundated with demands for constituent services. He said his small staff and some volunteers are kept busy researching material for speeches or position papers, assisting localities and constituents in dealings with the federal government on grants and other issues and keeping up with the political demands on his time.

For example, Robb heads a committee working to resolve a conflict that arose when a Pennsylvania shipyard rather than Virginia's largest employer, the Newport News Shipbuilding and Dry Dock Co., was awarded a multimillion-dollar contract to overhaul the USS Saratoga. He recently spent a day in New York City with Fairfax County officials trying to interest firms in locating in Virginia, and has traveled to Boston and Chicago for the same purpose. He has campaigned in West Virginia and North Carolina on behalf of Democratic candidates. And he gets as many as 25 requests a week to appear at state and local bipartisan functions.