WITH AN INTRIGUING new twist, the chase is on for governor of Maryland: Stephen H. Sachs may finally have found a way to get William Donald Schaefer's attention. If Parren Mitchell, dean of Maryland's black elected officials, agrees to run for lieutenant governor with Mr. Sachs, the first people to storm the hustings in a hurry will be the pollsters -- who have had Mr. Schaefer as the strong favorite all along. Mr. Mitchell is a longtime political favorite himself, and his addition to the ticket would clearly be a boost to the Sachs campaign.

Until now, Mr. Schaefer has been able to resort to an old political tactic of office-holding "frontrunners": don't let the challenger share a stage with you -- and certainly not for a debate. The mayor of Baltimore has been running for governor as if he already had the job. At least Mr. Sachs, as Maryland's attorney general, can claim to hold state office already. But Mr. Schaefer does have a compelling reason not to get bogged down in debate with his opponent: the mayor has his hands full debating himself -- figuring out which of his stands to stick with on issues such as the Chesapeake Bay, the need for additional financing to aid local education and gun control.

At last count, Mr. Sachs had accused Mr. Schaefer of ducking more than 20 chances to appear with him. Sachs supporters were offering a reward to any organization that could successfully sponsor an hour's debate somewhere in the state. In the meantime, Mr. Sachs has been hammering at the mayor's record in Baltimore, accusing Mr. Schaefer of lavishing city resources on the "glitz and glitter" of the Inner Harbor while ignoring the dimensions of poor housing, teen-age pregnancy, school shortcomings and poverty. Congressman Mitchell, too, has voiced the same criticisms. With Mr. Sachs apparently climbing in the polls -- if only from 3-to-1 underdog to 2-to-1 -- Mr. Schaefer might see fit to consider a joint appearance to rebut the Sachs accusations.

Maybe Mr. Schaefer's popularity as mayor will be enough to win him a promotion without much explanation of his thinking on state issues. But in the coming weeks Marylanders just might want to know a lot more about how Mr. Schaefer would handle taxes, social programs, the state budget, relations with the legislature, the complexities left in the wake of the S&L mess -- as well as a face-to-face challenge from a vigorous opponent.