The Prince George's County attorney filed briefs yesterday strongly defending a tax-cutting charter amendment that, if passed, will severely cut the amount of revenue received annually by the county government.

The briefs allege that a lawsuit aimed at removing the amendment known as TRIM (Tax Relief Initiative for Marylanders) from next Tesday's ballot was filed too soon because there is no reason for the court to make a ruling on the constitutionality of the referendum until it is approved by voters.

At the same time, County Attorney James C. Chapin argued in the briefs that the suit was filed too late, because the TRIM referendum was placed on the ballot in August, but no challlenged until October.

The county attorney contends that if Judge George W. Bowling, who is scheduled to hear the case Friday, grants the temporary injunction to take the referendum off the ballot it will in effect be a final injunction because the county would not have time to appeal before Tuesday's election.

Calvert Steuart, one of two attorneys who filed suit against the referendum, said yesterday he had not seen the briefs and would prefer not to comment until he had read them.

The County attorney contends that if Judge George W. Bowling, who is scheduled to hear the case Friday, grants the temporary injunction to take the referendum off the ballot it will in effect be a final injunction because the county would not have time to appeal before Tuesday's election.

R. Calvert Steuart, one of two attorneys who filed suit against the referendum, said yesterday he had not seen the briefs and would prefer not to comment until he had read them.

While the county was filing its briefs yesterday David Bird, coauthor of TRIM, was filing a motion to intervene, requesting that he be allowed to help the county defend TRIM in court Friday on behalf of those who signed the petition. Stuart said he would not object to that motion.

If Bowling orders TRIM off Tuesday's ballot, it cannot be reintroduced until 1980 because referendum can be voted on only during general or congressional elections.

The TRIM referendum, which would freeze the county's total propoerty tax levy at the amount raised for the 1979 budget or about $140 million, has been endorsed by virtually every political candidate and special interest group in the county, including County Executive Winfield M. Kelly Jr. and his Republican opponent, Lawrence J. Hogan.

Samuel S. Pickett, the other lawyer who filed the suit agianst TRIM, said the suit was filed on behalf of apartment owners in the county who felt it would be the first step toward a tier tax - currently illegal in Maryland - that would allow the county to place higher property taxes on apartment owners (landlords) than homeowners.