William K. Weaver left the Statehouse last week a happy man. So did Thomas C. Bradley. Even happier was Cheryl D. Lynch. And Janet C. Hoffman. And Blair Lee IV.

Jean Heald was probably the happiest of all.

Weaver, executive director of the Maryland Bankers' Association, was a big winner during the 90-day session here, taking home higher interest-rate ceilings on consumer loans and credit card charges.

Tom Bradley, president of the Maryland-D.C. AFL-CIO, took home higher benefits for the unemployed. Cheryl Lynch, of Associated Catholic Charities, took home a long-awaited adoption bill, welfare benefits for pregnant women, and migrant farm worker legislation. Hoffman, the lobbyist for Baltimore, got a one-year bond extension on the inner city's deteriorating Memorial Stadium. Blair Lee IV, Montgomery County's lobbyist, took home dollars for a highway interchange.

And then there was the higher legal drinking age, which Jean Heald of Mothers Against Drunk Driving (MADD) took home after the legislature broke from its five-year-old tradition of rejecting such legislation.

When the 188-member Maryland General Assembly adjourned last week sine die, legislators and Gov. Harry Hughes could go home happy too. They had eked through the 90-day session without alienating the key lobbyists and special interest groups that descended on the Statehouse last January bearing lengthy wish lists of election-year legislation.

These groups--the bankers, labor, the Catholic Church, and some local governments, in particular--had among their best legislative years ever. And Hughes and the legislators, who greeted the 1982 session apprehensively--it had all the ingredients for a political nightmare--were glad.

On the surface, of course, all of the politicians publicized the "unpopular" election-year legislation they had enacted. They emphasized the "discipline" of the session, noting repeatedly that controversial issues were weighed on individual merits (and not traded or bartered for other bills), an uncommon phenomenon in a year of high political tensions.

The assembly, with the governor behind it, approved a higher gasoline tax and higher interest-rate ceilings and raised the drinking age. Surely legislators could not be accused of stooping to their basest political instincts.

But what they also accomplished was to win some important friends in time for the November elections. And, surprisingly, they managed to do it by moderating between competing interest groups while avoiding the ire of any one strong political force.

The legislature's success in placating the powerful special interest groups was partly the result of the lobbies' growing sophistication and experience. The Catholic Church lobbies, which have come to command new respect among politicians, became the undisputed leaders in pushing for (and winning) social welfare legislation. The bankers, with fat expense accounts and a history of generous campaign contributions, were understandably well-received in an election year. And labor made its presence felt with a surprisingly well-attended Solidarity Day rally at mid-session, which legislators could not hope to ignore.