The Democratic primary race to nominate a candidate to succeed Gov. William Donald Schaefer has yet to produce an odds-on favorite. But Mayor Kurt L. Schmoke's enthusiastic endorsement of Parris N. Glendening yesterday is an important development. It gives the professorial Prince George's County executive a highly visible cheerleader in a populous and heavily Democratic area where he must perform well if he hopes to win the Sept. 13 primary.

When Mr. Schmoke made his endorsement at City Hall plaza, he rolled up his sleeves to underscore his commitment. Larry Gibson, the mayor's political strategist and behind-the-scenes facilitator, explained the gesture by saying the Schmoke camp would do "absolutely everything" to assure the victory of Mr. Glendening. In return, we hope the mayor got assurances Mr. Glendening would do "absolutely everything" for Baltimore City if elected.

There will be those who want to belittle the significance of this event. Yet the undeniable fact is that Mr. Glendening has garnered the single most important endorsement of the campaign thus far. Mr. Schmoke's help is likely to make the Washington area politician much better known in the Baltimore region -- the main base for another leading Democratic candidate for governor, Lt. Gov. Melvin A. Steinberg. Mr. Glendening has been doing quiet organizing in Baltimore for the past two years, but until Mr. Schmoke's announcement he had gotten relatively scant attention here.

We hope that this development energizes the other campaigns so that a real contest develops. Marylanders deserve an exciting, substantive race in which the issues of the day are debated and the merits of the candidates compared.

This also means that Mr. Steinberg must shift his seemingly disorganized campaign into higher gear. Meanwhile, Sen. Mary H. Boergers must make herself better known beyond her Montgomery County turf, and Sen. American Joe Miedusiewski has to make himself credible outside East Baltimore. Businessman Stewart Bainum Jr., of Montgomery County, has to make up his mind.

The clock is ticking. Almost anything can happen between now and the primary. But one thing is certain: The mayor's endorsement is a big boost for Mr. Glendening.