Last Saturday was "TRIM Plus Signature Day" in Prince George's County.

At shopping malls throughout the county volunteers solicited signatures to place an amendment on the ballot that would modify TRIM, the charter amendment that freezes the amount of taxes the county can collect, so that more tax money could be raised.

To place the amendment on the ballot, 10,000 signatures are needed. By the end of what was to be the final push on the petition drive, only 900 new signatures had been gathered.

To the organizers of the drive it was convincing evidence of what a number of politicians have already discovered: People in Prince George's like TRIM just the way it is.

Now, after six weeks of effort, the group of business, labor and community, leaders who have been trying to get TRIM Plus, the measure to modify TRIM, on the ballot are debating whether to abandon their effort altogether. t

Members of TRIM Plus blame a recently approved 35-cent reduction in the property tax rate -- the second tax rate cut since TRIM became law -- and the lack of support from politicians for the lack of success. In all they have gathered only 4,000 signatures.

"The timing was all wrong for this effort," said one member of the modification committee. "The way TRIM is written is asinine but you can't tell the voters that with a 35-cent tax cut."

Said another committee member, "It may be best to let the thing [modification effort] die an unpublished death."

Joanne Brown, cochairman of TRIM Plus who also heads the county Council of PTAs, said yesterday that the entire group will get together Monday to decide "whether to continue the effort and if we want to continue what strategy we should pursue."

Since 1978 when TRIM was passed overwhelmingly, the county has been prevented by law from collecting any more tax dollars than the $142 million collected that year.

As a result, the county property tax rate has been dropping, but so too have the number and extent of county services, with cutbacks most severe in the education and park systems.

The modification proposed by TRIM Plus would allow tax collections to rise slightly with inflation and would also allow the county to tax any new development without such taxes being included under the $142 million ceiling.

Brown criticized many of the county's elected officials who previously indicated they supported a modification of TRIM but have since backed off because of the continued high popularity of TRIM.

"It would be political suicide to go out there now saying TRIM is bad," said one county council member who asked not to be named. "How could you justify that?"

While publicly many county elected officials, all of whom endorsed TRIM in 1978, say they favor keeping TRIM as is until the 1982 election year, many of them admit privately that TRIM, if unmodified, could seriously harm the county's delivery of services in the next year or two.

Last year, the first year under TRIM, the county government reduced the tax rate 28 cents from $3.32 per $100 of assessed value to $3.04 -- to conform with the requirements of TRIM and were forced to cut back park hours, reduce the number of classroom teachers and close several county schools.

This year, the county avoided an expected fiscal crisis and serious curtailment of services and was able to cut taxes again because of a massive infusion of state aid that is not expected to recur next year.

Brown said that if the state is unable to continue providing large sums to the county, Prince George's will quickly find itself "in a crisis situation. If you modify TRIM and allow for a little growth you avoid the crisis and you also continue to keep a hold on government spending."