Maryland Senate President James Clark Jr. officially conceded the loss of his powerful position today, informing Sen. Melvin A. Steinberg that he will not challenge him for the presidency at Monday's Democratic caucus.

Clark's announcement was the first step in a transition of power that is expected to create a more liberal, aggressive senate than the one over which Clark presided.

Steinberg, the feisty Baltimore County lawyer, and Clark, the laid-back Howard County farmer, met for 30 minutes to discuss Clark's role in a Steinberg-run Senate.

"As a former president, Jim deserves special treatment," Steinberg said. "But I admitted to him that I was concerned about . . . his supporters still looking on him as president and creating a situation where there are almost two presidents."

To Steinberg's delight, Clark did not put Steinberg in the uncomfortable position of requesting a place in the new senate leadership.

Clark asked for a position on the Economic Affairs Committee, noting that it is "the only committee I've never served on so I thought I might find it interesting. Mickey told me that was fine. "I don't think he wants any trouble from me. He's got enough trouble as it is."

Steinberg's main problems could arise from a senate divided by the bitter battle for the presidency and from the fact that he had to make so many deals to line up the votes needed to defeat Clark.

For example, one of the centerpieces of Steinberg's campaign was a promise to eliminate the Constitutional and Public Law Committee as a way of strengthening the other four standing committees. But because chairmanships and vice-chairmanships were barter, the committee, considered unnecessary by most senators, will remain.

Steinberg said he plans on being a more activist president than Clark.