WHILE TRIM WAS nothing more than an election issue in Prince George's County, it was pretty intoxicating stuff. Under the influence, so to speak, the candidates did some pretty heady fiscal promising. But now comes the inevitable morning after, and a certain throbbing sensation seems to be setting in. First, there is that budget surplus that County Executive Winfield Kelly Jr. said he anticipated back when he was endorsing TRIM - about $20 million, voters were told. County officials are now saying that more than half of that $20 million may not be there at all. That would seem to mean that incoming County Executive Lawrence J. Hogan may have to prepare next year's budget with $11 million less than Mr. Kelly had said was necessary to continue "the delivery of basic services."

Then there is Mr. Hogan's campaign promise to cut the county budget. At the time, he said he had a study showing how he could cut between $33 million and $43 million from the proposed $443-million budget. Well, now we're not all that sure, it seems; "maybe I'm wrong," said Mr. Hogan, stressing that he'll try to keep his word. He, too, had kind words for TRIM during the campaign. Now, says the executive-elect, "It definitely is going to be a big challenge to live with TRIM . . . If we end up in a situation where TRIM forces us to cut into muscle, rather than fat, then we'll have to take another look at it."

One voter's "fat," of course, is another's "muscle" - which is precisely the dilemma caused by TRIM. What TRIM does is freeze total annual property-tax collections, which make up one-third of the county's revenues, at this year's level. This year's level, voters heard during the campaign, was projected to be about $140 million. But now comes an estimate that the figure will be closer to $132 million. And it isn't clear whether TRIM requires the county to freeze its collections at the amount actually collected this year , or at an amount including future accruals.

In the fat-and-muscle department, votes are only beginning to see how budget cuts may affect county government services. Early word has it that cuts are being proposed for programs aiding the elderly and the handicapped. And while TRIM may not apply legally to the County Planning Board's tax rate, the board has reacted with proposals to cut recreation programs - a shortened summer-playground season, shorter hours at community centers, elimination of field trips for preschool children, elimination of preschool, transitional and after-hours programs for disabled youths, and so on.

This may just be the first round of an old bureau-cratic game in which there are proposed cuts of police officers, fire fighters or teachers or anything else that is likely to generate enough public outcry to excuse a bigger budget. Only this time, the money would hage to come from a source other than the property tax. That's the trouble with TRIM and other arbitrary, rigid limits; they have a certain, immediate, intoxicating appeal. But in the cold light of the morning after, it becomes painfully clear that over time a price must be paid. The price in the case of Prince George's is almost inevitably going to be less self-determination at home in the county and a greater need to turn more often for help from the state government.