NO MATTER how lean the taxpayers of Prince George's County may like their budgets, the fiscal facts of life under TRIM (the Tax Reform Initiative for Marylanders) lead to a old budgeteer's rule of accounting: when a bottom line hits a ceiling, something's got to give--and usually it's the taxpayer. That's the story today in Prince George's, and it is the reason behind Plus 4, a sequel that will be on the ballot in November. This latest proposal would modify TRIM by allowing the county council to increase by up to 4 percent annually the amount of property tax revenues collected.

Without Plus 4, the equation won't work: TRIM plus inflation equals not enough. That's because the old limitation simply froze the total dollar amount of money that could be raised through real estate taxes at the 1979 level of about $143 million, period. At first, that wasn't the end of the world for county services--and in fact, many who opposed TRIM now acknowledge some fruits of frugality in retrospect. But this week, the county council responded to a growing sentiment that some relief valve had to be created, if for no other reason than to meet inflation.

A petition drive to put Plus 4 on the ballot has been under way for some time; the other day the county council by a 10-to-1 vote approved legislation that will ensure its appearance on the ballot. Some people may find Plus 4 not enough, and some have said it flies in the face of the popular demand that approved TRIM in the first place. But that first place isn't now, and popular sentiment could stand a review. Besides, even if Plus 4 is approved, its application would still be up to the council. Without it, the room to maneuver becomes a closet.