The Prince George's County Council approved legislation yesterday that clears the way for a vote this fall on an amendment to the county's charter-mandated cap on property tax revenue.

If approved by the voters in November, the new proposal, known as Plus 4, would modify TRIM (Tax Reform Initiative by Marylanders), an amendment to the county charter overwhelmingly approved by voters in 1980 that placed an absolute limit on property tax revenues. The change would allow the County Council to increase by up to 4 percent annually the amount of property tax revenues. Currently the county may collect only as much revenue from the property tax as it received from that source in 1979, or about $143 million. The amendment to TRIM also would permit increases in revenue resulting from new construction.

Council members passed the Plus 4 charter amendment 10 to 1 after a two-hour public hearing. The forum was dominated by union leaders, teachers and members of the various county Parent-Teacher Associations, nearly all of whom referred to the layoffs of 500 teachers this spring.

The council, wading through a marathon agenda, also approved the "Pac-Man bill" that raises the tax on video game machines from 2 percent to 5 percent, and introduced an emergency measure to grant tax relief to the ailing Washington Capitals hockey team.

The Pac-Man tax was approved as an emergency measure to raise $400,000 to $600,000 for the schools in the wake of the layoffs.

The tax relief package introduced at the request of Caps owner Abe Pollin will allow the hockey team during the next three years to pay an amusement tax of only one half of one percent instead of the regular 10 percent. In years four to six, the rate will gradually increase until it reaches 10 percent. That measure comes up for final action Aug. 24.

Most of the two dozen persons who testified on Plus 4 blamed TRIM for the massive cutbacks in school funding in the fiscal 1983 budget that forced the teacher layoffs. Some warned that unless TRIM is modified, other services will be cut and the quality of life in the county will deteriorate.

"The county is being torn apart by competing interest groups," said Joslyn Williams, president of the Metropolitan Washington Council of the AFL-CIO, which has 65,000 members in Prince George's. "The entire metropolitan area is being treated to the spectacle of old versus young, poor versus middle class, government employe versus government employer."

Only two people spoke against modifying TRIM. One of them was James Gleason, a spokesman for the group that drafted and lobbied for TRIM two years ago. Gleason said the revenue cap would not need to be modified if the school board would "cut the fat" from the education budget. Should Plus 4 appear on the ballot, he said his group would work for its defeat.

"We'll tell the citizens that a TRIM report on the school budget identifies extreme waste, duplicate services, and poor management," said Gleason in prepared statement.

Council member Sue Mills was the sole dissenter on Plus 4, saying that "in the passage of TRIM the public said, 'Don't raise our property taxes,' and this is just what this does."

Yesterday's action, drafted by County Council chairman Gerard McDonough, assures that the Plus 4 proposal will be on the ballot in November, even if a referendum drive now in progress falls short of the required 10,000 valid signatures. McDonough said he introduced the bill at the request of the citizens who are collecting signatures, as insurance in the event the signature drive is subjected to "legal challenges."

"The courts over the years have not liked government by referendum," said McDonough. "They interpret the laws very strictly, as to wording and so forth. You always stand the chance of losing your access to the ballot."

An amendment to the bill says that if the collected signatures are accepted by the Board of Elections Supervisers, that version of Plus 4 will appear on the ballot and the council's bill will be withdrawn.