Representatives of Prince George's County's 6,000 teachers voted overwhelmingly last night to reject a two-year contract offer from the Board of Education providing for 9 percent raises next year and up to 7.7 percent the following year.

The 300-member faculty representative council of the County Educator's Association, called together one day before the end of the school year, objected that the complicated settlement offer did not meet teachers' demands for a double-digit wage increase and adequate provision for lowering class sizes. Moreover, many representatives said they would not have enough time to discuss the offer with their members.

The union's 11-member executive board later agreed with the representatives and voted to reject the offer, reversing a previous resolution to put the settlement before their membership for a mail-in vote that would have taken two weeks. The executive board will consider further action in the protracted contract negotiations today.

Negotiations for a new contract to go into effect Aug. 1 started last November when the Educators' Association wought a 42.4 percent salary increase. In February, after teacher sickouts protesting the board's salary offers closed several schools in one week, the negotiations deadlocked, with the school board offering an effective 6.8 percent increase and the union asking for 12 percent. The bargaining was declared at impasse by Maryland School Superintendent David W. Hornbeck and submitted to a three-member panel, whose long-awaited report was submitted to the parties last Friday.

The rejected proposal, offering somewhat lower raises than the panel, was hammered out between School Superintendent Edward J. Feeney and union President John Sisson last weekend. Sisson and Feeney initialed a tentative agreement, but the union's 11-member executive council voted to place it before the faculty representatives, many clearly angry at the terms, would do. "I brought them what I thought was a reasonable proposal. Evidently the representative council feels differently," he said.

Paul Pinsky, one of the more militant teachers who was recently elected to the union's executive board said "we've got to have recourse for 34 or 36 kids in an English class. The county has the highest class size limits in the area and is consistently violating that," he said.

School spokesman Brian Porter called the proposal reasonable in light of the budget restraints imposed by the County Council.