Not long ago, Lee Perlman, the Common Cause lobbyist at the Maryland General Assembly, was summoned to the private office of Acting Gov. Blair Lee III.

Half amused, half awestruck, Perlman, who leads the self-styled citizens' lobby here, sputtered as he glanced around the inner chambers: "Gee, I've never been here before . . ."

Those present howled with laughter. Common Cause, despite its energetic lobbying, has had few supporters in the legislature, much less a pipeline to the former adinistration of suspended Gov. Marvin Mandel.

The man who got Perlman in to see Lee was Del. David L. Scull of Montgomery County - a Democrat, a liberal, a Common Cause advocate, a public interest lawyer - who happens to be Lee's nephew.

In many families, you would naturally expect that sort of thing - a nephew with special access to an uncle. But in the Lee-Scull clan, headed by the acting governor's father, Col. E. Brooke Lee - once the powerful leader of Montgomery County's defunct Democratic machine - "politics is thicker than blood," as one relative wryly put it.

Scull's late father, David Scull, who was the Republican chairman of the Montgomery County Council, and his mother, Elizabeth Lee Scull, who now is council chairman, albeit a Democrat, have been known to defy party and family to oppose social and political injustices they deemed intolerable.

Young Scull has gained a reputation in the legislature as an intractable idealist, who is somewhat afield from many of his more practical-minded colleagues. Respected as "brainy," he's also seen as a "screwball," someone who makes unrealistic propositions to the legislature, accordin to some of his colleagues.

But constituents in Montgomery County, Scull contends, "expect you to come down her to be brokers for new ideas."

So when his uncle became acting governor, the 34-year-old Scull paid a visit to the executive office and spilled some of his thoughts on what be thought the legislature should be doing. Lee, in response, asked Scull and Perlman to help formulate an ethics package.

More broadly, Scull has become an informal consultant to the acting governor. "Dave's been a big help representing an important part of the spectrum: consumer issues, Common Cause and Liberalism," said Blair Lee IV, the acting governor's son and campaign aide.

"There's a need to have that input. Dad recognizes it and leans on Dave for it. Also, he's trustworthy as a member of the family."

Lest Lee, who wants the Democratic gubernatorial nomination, he criticized as getting too cozy with a liberal ideologue, his advisers emphasize that Scull's role is a limited one. They stress that Scull, who lives in Chevy Chase, is not the acting governor's "man" in the Montgomery County delegation, which represents Lee's home base.

Considering the patently individualistic Montgomery County legislators, caution from Lee's advisers is not without reason. The last politician who tried to impose anything on county Democrats was Lee's father, and he eventually was toppled by the growing force of independent-minded voters.

Meanwhile, Scull wryly observes all this, while heeding his father's political admonition: "Do what you can while you're in and try to have a good time."

"I have a lot of fun being in the legislature," said Scull. "I especially like legislative problem-solving and working out big solutions. This is a special place to be in local government because the population is very progressive and creative. It generates a lot of interesting improvements in the science of government."

This year Scull has introduced a bill that would cut the 176-member legislature in half and would extend the 90-day session to a full-time operation after 1987.

Large legislatures, Scull argues, have become "pretty invisible" and are too big to force complex policy.

The need for a full-time session is based on some calculations Scull made. According to those calculations, each legislative committee spends an average of 11 minutes on each of the 3,500 bills introduced every year. Once a bill reaches the floor of either chamber, Scull estimates that each proposal is disposed of in even less time - an average of about 90 seconds.

"My first year here," he said, "I asked one of the oldtimers how long he thought it would be before we went full time. He said 10 years; I said I hoped it would be sooner."

Scull's proposals have met some resistance. Del. Charles Krysiak (D-Baltimore) who views his role as day-to-day power broking and taking care of constituents' requests, takes a dim view of Scull's proposal.

"Forget it. It's a bad idea," said Krysiak. "The people aren't ready for it, and I don't think the legislature should be bothered with it." That is Krysiak's way of saying the bill won't get out of the House Constitutional and Administrative Law Committee, which Krysiak heads.

But Scull said he never expected the bill to get past the committee anyway. In fact, some of his proposals - public financing of elections, "sunset" laws, which would eliminate unproductive state agencies, and legislation that would make it easier for people to handle their own legal affairs - rarely go far at first.

Those kinds of proposals, Scull admits, are designed mainly to plant new ideas, which he believes the legislature ultimately will accept.

"Legislation largely is an educational process," he says. "That's an important role to play - to be a broker for change."