The scene was set on Mount Sinai. There, God encountered Donald B. Robertson, majority leader of the Maryland House of Delegates.

"I have some laws here and I need someone to take a look at them," God said, handing the Ten Commandments to Robertson.

Robertson squinted, took another drag on his cigarette and nodded his head approvingly. "These aren't bad," he said. "I can rewrite them."

On this particular evening, God was played by William P. Somerville, the lawyer for the House Constitutional and Administrative Law Committee. Robertson was played by Del. J. Ernest Bell II, a member of the committee. At the committee's annual party, the skit was the highlight of the evening. No one laughed harder than Robertson, a Montgomery County Democrat whose nickname among his colleagues is, "The Prince of Punctuation."

But underneath the hilarity was a message. Robertson, who has never made any pretense about being one of the boys in the legislature, has nonetheless earned a unique position among the 188 members: He is considered the ultimate authority on the delicate subject of HOW to write a law.

That ability, combined with his role as the head of Speaker Benjamin L. Cardin's powerful leadership team, has made Robertson, at 51, one of the unseen cogs of state government. Some love him, others despise him. But all agree on the two reasons he wields power: He has an eye for detail--and Cardin's ear.

"I doubt that many of the delegates understand how much influence Don Robertson has on what goes on down here," says Cardin. "Don has played a major role in changing how the House is run, in changing the ethics laws and in making my leadership what it has been the last five years. Some people don't like to admit that because some of them don't like his style."

It is style, not substance, that makes Robertson controversial. Even his enemies grudgingly concede that he understands the laws, the procedures and the technique of writing a bill better than anyone. He has a prodigious memory, whether for the history of the annotated code or baseball trivia. What's more, his integrity is unquestioned; he was a major influence in writing the state campaign finance act as well as the ethics laws.

"Every legislature needs a Robertson," says former delegate Luiz Simmons, who fought Robertson at every turn during four years on his committee.

Just as important is Robertson's influence on the leadership as a representative of Montgomery County's interests. For years, Montgomery represented the "outs" in a legislature dominated by old-school politicians, many of them from Baltimore. Now, with Robertson as Cardin's No. 2 man, Montgomery has a voice in the inner sanctum.

"We argue all the time," Cardin says. "Sometimes, Don drives me crazy because he never lets go of an issue. But he's effective that way." At least in part because of Robertson's presence, Cardin's leadership has pushed for many of the reform laws passed in the last five years: ethics, campaign finance, open-meetings--all issues Montgomery County had previously championed unsuccessfully.

But because Robertson is often rigid and uncompromising, because he insists on dissecting every piece of legislation, literally down to its commas, and because his shy nature often makes him seem aloof and distant, some colleagues delight in ridiculing him.

Admirers concede that Robertson is easily misunderstood because his intensity level is so high. "People look at Don and see the kid in school who reminds the teacher that she forgot to give the class homework," says Del. American Joe Miedusiewski, a member of Robertson's committee who admires him. "He loves the legislature and he can't understand people who don't take it as seriously as he does."

Cardin chose Robertson as majority leader five years ago because he wanted to reshape the floor leader's role, make him captain of a team that would reach all corners of the ideological spectrum. In five years, Cardin-Robertson have never lost a bill.

When leadership takes a position on a bill, Robertson is one of five men who divides up the delegates to find out where they stand and, if necessary, to pressure them into voting leadership's way. He is the liberal in Cardin's cabinet, the antithesis of Baltimore Del. Paul E. Weisengoff, who, although he holds no leadership position, has been Cardin's "other" majority leader.

Carefully, Cardin has placed Robertson, the good-government liberal from Montgomery County, on one side of him and Weisengoff, the slick Baltimore pol, on the other. If Cardin needs a bill sold on its merits, Robertson is his man. If he needs to trade some votes he sends for Weisengoff.

"One of the things I had to prove as majority leader was that I could communicate with the more conservative elements of the House," Robertson said recently. "I think I've accomplished that and in doing so I've proven to people that Ben was right to choose me."

More important, Robertson has proven to Robertson that Cardin was right to choose him. That may have been his toughest job.

For more than 20 years, Donald Brackett Robertson didn't give a hoot about politics or government. Growing up in Chevy Chase, he was an unadulterated jock, a kid who lived, breathed and ate sports.

He was born Oct. 6, 1931, or, as he puts it, "Fourteen days before Mickey Mantle," the first of two children born to Nathan and Elizabeth Robertson.

His grandfather was a Republican who was appointed U.S. commissioner of patents by Warren G. Harding. His father was a newspaper man, a White House correspondent, and a die-hard liberal. Robertson vividly remembers Sunday dinners at his grandparents' house where his father and grandfather would scream at each other about politics.

He collected baseball cards religiously (he still has many of them stored in his attic) and, in his last two years of high school, blossomed as an athlete when he finally grew, reaching 6-foot-1 and about 170 pounds. He chose Oberlin College because it was a good school where he knew could play varsity football and baseball.

The week after Robertson finished his freshman year of college, his father committed suicide at age 47. Nathan Robertson was a driven, intense man, unhappy in his later years. His last prolonged conversation with his son was about Don's switch from halfback to end on the Oberlin football team.

Robertson, at home, was awakened in the middle of the night by his mother. "I can't find your father," she said. Together, they went to the garage. There, they found him.

After college came the Navy and then Columbia law school. There, Robertson met Marian Ostrom. She was bright, attractive and, perhaps most important for the painfully shy Robertson, "someone I was comfortable with."

Robertson remembers his first evening with her for two reasons: He knew he had found the girl of his dreams and he misjudged a line drive in a softball game.

"I wasn't too impressed when I first met him because he was holding this dumb baseball," Marian Robertson says. "Then, he threw it to me and, naturally, I missed. When I reached down to pick it up, I put my heel through my new coat. Not exactly love at first sight. But after that evening talking, I told my roommate, 'This is the one.' "

Today, they have four children, ages 21, 18, 15 and 13.

Robertson set up his law practice in Washington and became peripherally involved in politics, working in Blair Lee's 1962 U.S. Senate campaign, the Johnson-Humphrey campaign in 1964 and the Humphrey presidential campaign in 1968.

"I think I knew when I got out of law school that I would like to run for office someday but I never thought I would," Robertson says. "I hated speaking in front of people. I thought I could contribute but I never thought I would have the opportunity."

The opportunity came in 1970 when Montgomery Democrats were forming a slate from the western part of the county to challenge a group of incumbent Republicans. There were seven seats available. Robertson ran fifth.

It was not an easy campaign. The first time Robertson went to a Democratic club meeting he insisted his wife go with him. "He was so shy he wouldn't go alone," she remembers.

Within a month of arriving at the State House, Robertson knew he was in love. "Nothing has ever stimulated or fascinated me the way this process does," he says.

Sen. Laurence Levitan, also a freshman delegate then, was one of Robertson's house mates that first year. "I would come home at three o'clock in the morning and Don would still be awake, reading bills," Levitan remembers. "I'm not sure he ever slept the whole 90 days."

After his first year, Robertson was elected delegation chairman, a job he held seven years. He was a controversial leader. Robertson insisted that delegation meetings be held late on Monday night, after the evening legislative session. While other members wanted to partake of the Annapolis night scene, Robertson wanted to amend bills until the wee hours.

"It took Don a while to figure out that he couldn't impose his own standards on everyone else," says Del. Helen L. Koss (D-Montgomery), Robertson's best friend and legislative alter-ego. "He's the hardest working guy I've ever known. But not everyone is Don."

Koss is so close to Robertson that Sen. Howard A. Denis (R-Montgomery) often jokes that, "I was here for three years before I knew Koss-Robertson were two people."

Koss is Robertson's devil's advocate and his sounding board, the one person in the legislature willing to work deep into the night writing amendments. Members of the Constitutional and Administrative Law Committee, which Koss chairs, affectionately call them, "Mom and Pop."

Recently, Koss-Robertson lost a fight over a bill involving the allocation of powers between counties and municipalities. They worked many nights on the legislation but committee members amended it so it did not come to the floor the way Robertson wanted.

Before the vote was tallied, Robertson felt compelled to tell the House he had voted for the bill but was not happy with it. "No one outside the committee knew what he was talking about, but he had to say it anyway," Koss said. "His intensity wouldn't let it go."

Robertson's intensity is usually written all over his long face. He has thinning brown hair, a constantly furrowed brow and a smile that explodes across his features when he is pleased or amused. Almost always, there is a cigarette in his hand. In the other is a cup of coffee. He is a two-pack and six-to-eight-cup-a-day man. When he relaxes, the coffee is replaced by scotch or white wine.

But Robertson never really relaxes. Even in his office where he will quickly shuck his jacket, loosen his tie and put on a blue sweater, he is always trying to do six things at once. Call a law client, sign a few letters, check his innumerable files. Each is neatly marked: "Floor," "Leadership," "Committees" . . . . "He is the ultimate perfectionist," says Del. Patricia R. Sher, his running mate the last two elections.

His wife and some friends believe he is a born teacher. "He would be superb," said Del. Michael Collins, a teacher himself. "Because if someone wants to learn, Don will spend 24 hours a day trying to teach them. He'll discuss an issue 50 different ways. He's intense about that, too."

It was his intensity that often put Robertson at odds with other members of the county delegation.

One of those Robertson clashed with was Del. Jerry H. Hyatt, now delegation vice chairman. "There was no give in Don then," says Hyatt, who now considers Robertson a friend. "He couldn't deal with people who didn't see things his way. I think when he became majority leader and had to deal with 141 people instead of 19, he changed. He's grown with the job."

He got the job because Cardin admired his indefatigability. An inveterate bill reader himself, Cardin asked Robertson to join the Ways and Means Committee, which he was chairing, in 1975. "Every day he was in my office saying, 'I can't stand this committee, all we talk about is money,' " Cardin remembers. "He kept saying, 'give me my freedom.' Finally, after two years, I did."

Back in Constitutional and Administrative Law, dealing with his true love, the annotated code, Robertson flourished. When Cardin became speaker in 1979, he ignored Baltimore friends who urged him to stay away from the Montgomery County white-hat image and made Robertson majority leader.

Today, the two confer at least a dozen times a day. There is a chicken-and-egg question here: Is Cardin an effective speaker because Robertson has done such a good job as majority leader? Or is Robertson's effectiveness as floor leader merely a reflection of Cardin's dominance?

"We won't know that until Ben's gone," says a Robertson friend. "If Ben's governor, Don will be up there with him. I don't think he'll be speaker. He's not a No. 1. He's the ideal No. 2."

On Robertson's 50th birthday several friends presented him with a large box. When he opened it, hundreds of commas and semicolons, cut out from newspapers, tumbled out.

That is one reflection of the Robertson image: the protector of the code, lover of punctuation, a man up to his chin in bureaucratic detail.

In Robertson's office is another gift, this one from his children. It is a poster of Snoopy, walking away from a baseball game, shoulders drooping. The caption reads: "It doesn't matter whether you win or lose . . . Until you lose."

That image, the intense competitor whose human side can be found with one look at his office, is more apt.

Robertson sums his approach up with a Mencken quote: "We face a number of complex issues in these times to which a number of solutions are offered. All of them are simple, appealing and wrong."

To Mencken's words, Robertson always adds an amendment: "We need to think harder about the problems we face, not accept the easy answers and struggle to find the right answers."

Naturally, Don Robertson knows the line by heart.