As a condition of going to work for the Associated Builders and Contractors trade association in January 1977, Lawrence J. Hogan agreed to renounce all political ambitions. It was a promise he could not keep.

When Hogan clashed with the association's president a year later, he decided not to fight a battle he says he could have won. Instead, he resigned to run for Prince George's County Executive against one-term incumbent Winfield M. Kelly Jr.

"I advised him not to run," said Gerard Holcombe, a long-time Hogan supporter. "I advised him to be a lawyer and make a lot of money. But just like an airedale at the fire house, when the bell goes off, he's ready to go. He could be an extremely wealthy man if it weren't for politics."

Once again, the public Larry Hogan had won out. A Republican propelled to Congress three times in a county that is overwhelmingly Democratic, he is a driving, magnetic and often combative politican, outgoing and gregarious. His present wife once described him as a "short dumpy guy," yet he nonetheless evokes the word "charisma."

The public Larry Hogan projects a dynamic image. He comes across as a man who is knowledgeable about a variety of subjects and is seldom at a loss for words. He is a good media candidate who enjoys the limelight. He is the man who says of himself, "I've always needed challenges in life."

The private Larry Hogan, often eclipsed by the public man, runs just as hard but does not enjoy the limelight. He is the man who, asked to name the toughest personal decision he has ever had to make, whinces noticeably and responds almost plaintively, "My personal life, I don't know that that's very relevant."

The pressure for full disclosure by politicians, the private Larry Hogan asserts, is "a deterrent to (entering) politics. You gotta let it all hang out. It's troubling to me."

A businessman's business is nobody's else's business, reasons Hogan whose private career has involved a variety of ventures, from public relations to land speculation. The latest venture hatched earlier this year. As he prepared to enter the county race, Hogan became first president, then general counsel, and a potential stockholder (as compensation "in lieu of fees") in corporations formed to market new technologies in waste treatment and energy recovery.

The moving force behind the venture is John W. Lyon. Lyon is president of Excavation Construction, Inc., a major contractor currently working on the Metro subway system and a firm whose activities are under scrutiny by grand juries here and in Baltimore. Hogan has represented Excavation Construction "off and on since I left Congress," Hogan said.

Larry Hogan's private portfolio also includes 2,437 acres of Pine Island, S.C., which particularly excites him, he said, because "Nobody's going to accuse me of conflict of interest." He and his wife and law partner, Ilona, also write and publish "The Hogan Report," a monthly potpourri of what's happening in the realms of politics and law. It sells for $24 a year.

Hogan's law practice has been more dormant than active during most of his career. He went to law school while working full-time as an agent for the FBI. Later, he opted for public relations over the law, building Larry Hogan Associates into a $1 million-a-year business.

His first client was the Washington Associatoin of Plumbing Contractors. He ran the organization and published its magazine for 10 years. Ocean Downs Raceway in Ocean City was another client.

"Public relations is a personal service by its very essence," said Hogan last week in the law library of his Forestville office. "If it were widgets, the company could have continued on." But widgets it was not, so, off to Congress, Hogan sold his business for a fraction of its estimated worth.

During Hogan's current campaign for county executive, he has tried to mute the strong conservative image he developed in Congress as a vocal proponent of the D.C. crime bill and an arch foe of abortion and busing for integration.

Hogan contends that his conservatism was never as strong as the media played it - he was an early supporter of full congressional voting representation for the District of Columbia - but his record reveals two zero ratings from the liberal Americans for Democratic Action.

Hogan's congressional career suffered, he said, from his inability, as one of 535 members and a majority party member at that, to change the course of history. In 1974, Larry Hogan the lawmaker made history by becoming the first Republican on the House Judiciary Committee to back the impeachment of Richard M. Nixon.

"I predicted it was going to kill me in the campaign for governor (which Hogan had entered that year) and I think it did," he said. "I suggested to my campaign manager I withdraw from the race and he talked me out of it. After Nixon resigned, I thought it would be an asset, but it wasn't."

Others attributed Hogan's 1974 primary defeat to his own campaign, which focused almost exclusively on Democratic incumbent Marvin Mandel instead of his Republican opponent, Louise Gore. It is the same strategy Hogan followed this year in the county race, with better results.

The 1974 defeat sobered Larry Hogan but did not crush him. "Every campaign, win or lose, I had a downer after it was over except for that one," he said. "In a way I felt relieved it was over. I did not have one day of depression."

For one thing, Larry and Ilona Hogan were expecting their first child in December of that year. "I had that to absorb me," he said.

Hogan also had financial problems stemming from a costly divorce from his first wife of 27 years. He tried unsuccessfully for a State Department post. There were also reports, denied by Hogan, that he sought to be named U.S. Attorney for Maryland.

Instead, he and Ilona opened the law firm of Hogan and Hogan, with offices in downtown Washington and in Forestville, in the John Hanson Savings & Loan building.

Hogan had never been admitted to the practice of law in Maryland. Admission required either passing the bar exam or practicing somewhere else for five of the prior seven years. Hogan advanced the novel argument that his congressional service, particularly his tenure on the House Judiciary Committee, constituted practicing law. The Maryland Bar did not accept the idea.

"They were worried about him, quite frankly," said Gerald Holcombe, who is also an official of the Hanson bank in which the Hogans own stock. "He's a popular, tough competitor."

While Hogan & Hogan divided its work along jurisdictional lines - Larry Hogan working in the District of Columbia and Ilona in Maryland - Larry Hogan began rebulding his political base in the state of Maryland. "I had it in the back of my mind I had a problem with a Republicans in Maryland, and I strived to remedy that," he said. In 1976, he succeeded by being elected Maryland National Republican Committeeman.

In January 1977, after negotiations that dragged on for six months, Hogan went to work as executive vice-president of the Associated Builders and Contractors, a lobby largely for nonunion firms who advocate awarding contracts to bidders regardless of their labor policies. In the current campaign, he has advocated binding arbitration for public employes, a position more popular with labor than management.

Gene Higgins, who was Hogan's assistant at ABC, described his former boss as "a strong executive," "a strong personality," who "increased the association's effectiveness."

Pressure to get back into politics, both self-generated and from others, contributed to Hogan's decision to leave the post that paid him between $70,000 and $100,000 a year. At the time, the chief executive spots in both county and state government were up for grabs.

At that time, the only Republican running for the county job was builder Martin Aragona, who was considered no threat to the Democrats.

Local Republican leaders hopefully eyed Hogan, the only Republican elected to Congress from Prince George's since the early 50s, a man with a strong personal appeal that somehow inspired county. Democrats to vote for him. "All our polls indicated he was the man to win," recalls former party chairperson Melissa Martin.

Hogan chose to run for county executive instead of for governor, he said, after "tremendous pressure from citizens, elected officials, county officials, Republican officials . . . I thought the voters should have a choice."