WHEN MARYLAND Gov. William Donald Schaefer announced the beginning of a long study of the state's tax structure, you could hear the groans in Montgomery County and see the frowns in Prince George's. There, as in other relatively wealthy pockets of the state, any fiscal exercise by the former mayor of Baltimore sets off an alarm, given his many pointed comments about the wealthier counties and his love of financing formulas that do well for Baltimore City at the expense of the Washington suburbs. Others could note from experience that studies tend to be great burial grounds for difficult projects. Should Marylanders expect any constructive financial action from this one?

We'll see -- but there are reasons to believe that the governor really wants a serious financial inventory and projection that would go well beyond his years in office and that would lead to sound revision of the state's tax structure. To begin with, he has tapped a Montgomery County lawyer with a long record of distinguished public service, R. Robert Linowes, who swears he can't stand "study commissions unless they can put into effect realistic, useful policies -- specific proposals for legislation. We could do a simple report in six months, but the governor is talking about doing serious research, developing a sense of where Maryland is going financially, into the 21st century."

Mr. Linowes says Gov. Schaefer has agreed to let him handle everything from membership of the commission and staff to research, periodic public reports and recommendations that would be completed by the legislative session of 1991. Already assisting in the direction of the project is an expert in the finances of the region, Philip M. Dearborn, vice president of the Greater Washington Research Center. The study will include assessments of changing federal assistance, of the economies of every county of the state as well as Baltimore City and of shifts in populations and demands for services within the state.

This is hardly the kind of activity that will capture the daily attention of Marylanders, but if it does lead to long-overdue revisions of the state income-tax structure as well as the formulas for distributing the pot, the project will succeed where past intentions, announcements and commissions haven't. Taxpayers at least should hope that Gov. Schaefer's idea lives up to its advance promotion.