When Lawrence J. Hogan left the U.S. House of Representatives in 1974, he took with him a record of three straight zero ratings on the congressional scorecards compiled by Americans for Democratic Action. He also took this epitaph from a liberal colleague: "Larry looks pleasant, talks like a moderate, and votes like a neanderthal."

Four years later, that colleague might have a difficult time recognizing Hogan. In the last two months, as the Republican candidate for Prince George's County executive, the 50-year-old former FBI agent has taken up the causes of groups that have traditionally turned to liberals and Democrats for support - labor unions and working women.

While Hogan has been cultivating these unlikely constituencies, his Democratic opponent, incumbent County Executive Winfield M. Kelly Jr., has concentrated on issues more often associated with Republicans - reduced budgets and tax cuts.

Hogan, who made his name in Congress by opposing school busing and championing the law-and-order theme of his former boss, the late FBI director J. Edgar Hoover, now says that he was never as conservative as many people assumed.

"I dislike labels and I've always thought people misunderstood my record in Congress (from 1968 to 1974)," Hogan said yesterday. "People don't remember that I was an early supporter of voting rights for the District of Columbia and that I supported ERA. I really don't think I'm doing anything this year that I hadn't supported in the past."

Kelly, meanwhile, argues that his almost exclusive emphasis on fiscal issues this year does not mean that he has abandoned the social programs created by his party. He dismisses as posturing Hogan's recent statements on such issues.

"I think Larry is trying to say all things to all people," said Kelly."He's trying to cover the entire ideological spectrum just to get elected, but I think it's going to catch up with him."

At a press conference this week, Hogan directed his attention to the women's movement, arguing that the Kelly administration had a "terrible record on hiring women" and saying Kelly fostered polices that were "a hangover from male chauvinism." As an example. Hogan noted that of nearly 600 county employes earning more than $20,000 yearly, only 30 were women.

Hogan said that as county executive he would increase "very substantially" the number of women on the county payroll and attempt to create permanent part-time jobs for women with children to work between the hours of 10 a.m. and 2:30 p.m., when the children were in school.

Kelly responded that Hogan was "playing with the facts" in his pitch to women. According to statistics culled from the county personnel office, Kelly pointed out, 43 percent of the county workers hired since he took office have been women. In addition, he said, the number of women county employes earning $16,000 or more has jumped from 22 under the previous administration of Republican William Gullett to 106 under Kelly.

The 42-year-old county executive said he preferred using flexible work schedules - known as "flex-time" - rather than Hogan's idea of hiring women for part-time jobs with specific midday hours. "I think that would tend to force them into assembly-line or clerical jobs," said Kelly.

Hogan's bid to organized labor came last week when he announced his support of binding arbitration to settle contract disputes with public employe unions. To people who remembered that Hogan's last private job was as an executive for a national builder's lobby that opposed union shops, it was a surprising turn of events.

"I've always supported it," Hogan said last week. "For unions to survive, they've either got to have the right to strike or binding arbitration. I don't think they should be able to strike, so we can't rob them of all their power."

Kelly a wealthy businessman, said he opposed binding arbitration because it took away from elected officals the power to set salaries and thus, in effect, the power to control the county budget. He said he found it contradictory that "Larry, on the one hand say he'll cut the budget and then on the othe hand, wants to give away his power to control a major portion of the budget."

Despite his opposition to binding arbitration, a concept that is becoming increasingly popular in the labor movement, Kelly has the official support of a majority of Washington area labor organizations. Hogan, who has been endorsed by the county police union, claims that he has the support of most rank-and file workers.

Kelly has never had a particularly warm relationship with labor leaders, some of whom say that his attitude toward them is symbolized by the many meetings the county Democratic leadership holds at the Sheraton-Lanham, a hotel that for two years has been on the AFL-CIO's "unfair list" as a result of a long and complicated strike there.

"I think Kelly and the Democrats have made a conscious decision that wealthy developers are worth more to them than the need to deal with the Labor Movement," said Ron Richardson, of Local 25 of the Hotel and Restaurant Employees Union. "Hogan has not had a great record on labor, but he can't be worse than Kelly."

Hogan's conservative roots are more apparent in his support of the county police rank-and-file, who have protested Kelly's firing of Patrolman Peter Morgan, who shot and killed an unarmed, fleeing shoplifting suspect. Police union leaders say Kelly's action was an unwarranted attempt to placate the county's black community at their expense.

Hogan agrees with that assessment, saying that he would not have fired Morgan, and that in most such situations, he would 'give the benefit of the doubt to the policeman." Even on law and order issues, however, Hogan has taken one stance that does not sit well with the police - he supports the idea of putting a citizen on the police review board that examines complaints against officers. The police union has strongly opposed efforts by Kelly to place a civilian on the three-member panel.