Baltimore Mayor William Donald Schaefer continues to lead the race for the Democratic nomination for Maryland governor, holding a 31 percentage point lead over state Attorney General Stephen H. Sachs, according to a new poll.

However, the survey showed that Sachs has picked up ground since House Speaker Benjamin L. Cardin dropped out of the race. He was favored by 26 percent of those questioned, compared with 22 percent in a similar poll taken in October.

Schaefer's support -- 57 percent -- was up 4 percentage points from the previous poll. Eighteen percent of the 537 registered voters polled by Mason-Dixon Opinion Research Inc. between Dec. 9 and 14 were undecided.

The poll also says that Rep. Barbara Mikulski (D-Md.) has a considerable lead over the former front-runner, Gov. Harry Hughes, in the race for the Democratic Senate nomination.

If the Democratic primary were held now, Mikulski would get 33 percent of the vote to 18 percent for Hughes, 15 percent for Rep. Michael D. Barnes and 14 percent for Baltimore County Executive Donald Hutchinson, with the remainder undecided, the poll said.

The October poll showed Hughes with 29 percent support in the field of Democrats seeking the Senate seat being vacated by Republican Charles McC. Mathias Jr. The greatest drop in his popularity came in Prince George's County, where his support dropped 22 percentage points in the period between the two polls, and on the Eastern Shore, where his support fell 16 percent.