IT NEVER did involve dead-serious presidential ambitions, but up until last week, Maryland Gov. William Donald Schaefer was a sort-of candidate for president. The idea -- his as much as anyone's -- was to field a "favorite son" candidate in the March 8 Super Tuesday party primary, as a possible way to increase Maryland's impact on the selection of a Democratic nominee. The most available, most mentioned, most appropriately coy "son," as it happened, turned out to be Mr. Schaefer.

As a primary strategy with secondary considerations, the Schaefer "candidacy" initially drew polite comments from various elected officials about the value of party unity. But after a round of second thoughts, most of them concluded that the voters might well have some better ideas of their own -- and might not take kindly to a mass abdication of their voting options.

Besides, many of those officials whom Mr. Schaefer consulted have picked favorites rather than a favorite son: and one of the big favorites in Maryland at this point is Jesse Jackson. Most political pros in the state say that right now Mr. Jackson has a grip on the 5th congressional district -- which includes most of Prince George's County -- and the Baltimore-based 7th district, home of Rep. Kweisi Mfume, cochairman of the Jackson campaign in Maryland. Both districts went solidly for Mr. Jackson in 1984. His supporters note that nearly 25 percent of the state's registered Democrats are black, and that their campaign seeks to appeal beyond this group to all party voters.

An open field, rather than a favorite son and slates of uncommitted delegates, could work to Mr. Jackson's advantage in Maryland, particularly if other candidates' attention is focused on the rest of the states in the Super Tuesday lineup. But Maryland supporters of other Democratic candidates also have an obvious interest in a wide-open contest: they want to campaign for their own choices -- and nail down committed delegates. So nearly all the Democratic politicians in the state seem relieved that their governor has consulted with them and backed off the favorite-son idea. One reason may be that the fewer the favorite sons, the less chance (remote though it may be to begin with) that someone not in the active early running could end up with the nomination.