Prince George's County residents voted overwhelmingly yesterday to modify TRIM, a tight lid on property tax collections. The modification, government officials have said, will provide the county with $6 to $8 million in additional revenues next year for education and public safety.

Virtually complete returns last night showed that a majority of voters approved Question A, the charter amendment to modify TRIM, by a vote of 75,857 to 66,596.

The original version of TRIM (Tax Reform Initiative by Marylanders) was approved overwhelmingly by county voters in 1978 and had withstood one previous effort to weaken its effect.

TRIM had limited the amount the county could collect in annual property tax revenues to $143.9 million.

The change approved by the voters would lift that ceiling and instead freeze the property tax rate at $2.43 per $100 of assessed value. Thus, property tax levies and collections could rise as assessments increase.

County Executive Parris N. Glendening, who has said that the new money will go to ease the severely strained budget for education and public safety, praised the voters' approval of the modification amendment.

"This is a vote of confidence in the future of Prince George's County," Glendening said at a Democratic Party victory celebration in New Carrollton.

And Royal Hart, the county government's legislative liaison, who has complained about TRIM's negative effect on the county's ability to get fiscal help from the General Assembly, said he had expected the win to be a closer one.

"This shows that people in the county recognize that the ability of the county to provide essential services is more important than a few dollars saved on their taxes," Hart said.

Officials of FACT (Fairness for All County Taxpayers), the group which supported the charter amendment, have estimated that the change will cost the average taxpayer about $30 during its first year.

TRIM, the FACT forces argued, benefited large businesses with declining tax assessments and not homeowners, whose assessments have continued to rise. A rising property tax rate, they said, has not changed this equation.

TRIM supporters -- among them the amendment's original authors William Goodman and state Del. David Bird -- insisted that the measure had accomplished exactly what it was meant to do. County services, they said, have not suffered as much as government officials say.

Instead, TRIM supporters said, school spending per pupil continued to rise even as the system's population declined. They also said that because property tax revenues constitute only 24 percent of the county's budget, the county was not forced to rely on that money alone to provide services.

But Glendening blamed TRIM for giving the county the "largest class sizes in Maryland and the lowest teacher salaries in the metropolitan area."

Part of a wave of taxpayer initiatives that took hold across the country in the wake of California's Proposition 13, TRIM was the strictest such measure to win approval. Its boosters said it had given county homeowners some control over their own tax bills while at the same time forcing the local government to spend more efficiently.

"We think people have been deceived and confused by the wording of the amendment," said TRIM spokesman John T. Gleason. "When property taxes go up in the next couple of years, we expect voters to rejoin us in lobbying for another TRIM cap in 1986."

"I am so relieved," said Carolyn Scriber, a county worker who estimates that she worked 20 hours a week on behalf of Question A. "I truly didn't believe there was going to be this big of a margin."