The Prince George's County school board and the teachers union yesterday reached tentative settlement on a new contract giving the county's 7,000 teachers a 10 percent salary increase over two years and improved fringe benefits.

The agreement, made public by a spokesman for the teachers union, ends a threatened impasse in contract negotiations which would have automatically triggered outside arbitration. The tentative 25-month contract was approved overwhelmingly late yesterday by the 400-member governing council of the Prince George's County Educators Association.

The contract agreed on by negotiators still must be ratified by the teachers, who are expected to vote on it within two weeks, and by the school board. If approved, it will go to County Executive Lawrence J. Hogan, who must submit next year's budget

The board is under pressure from Hogan to hold the line on spending to the County Council by April 1, because a measure approved by voters at referendum last fall places a ceiling on property tax revenues.

School board officials declined to comment on the settlement, but Toby Rich, president of the teachers union, said the agreement came arter school officials sweetened their contract offer with increased fringe benefits such as tuition reimbursement for teachers taking graduate courses and improved maternity benefits.

The proposed 10 percent increase in teacher base pay, 5 percent this year and 5 percent at the start of the second year, would give most county teachers annual increases of about 11 percent since their pay scales have an average 6 percent increase based on the number of "steps" or years of experience.

Starting salaries for Prince George's teachers under the proposed contract would rise to $11,442 a year from the current $10,897, Rich said. Salaries for teachers with master's degree would go up to $13,730 from the current $13,076.

Also agreed on was a plan under which teachers' prescription drug purchases would cost no more than $2 each. Longevity steps and higher pay for senior teachers also were added and teachers would be given two free work days a year in which to do such things as grade papers.

"Considering the financial and political climate in Prince George's, this is a good contract," Rich said last night. "It's not everything we wanted but it will definitely help keep quality teachers in the school system." He also said he expected the contract would be "fully funded," meaning he expects that the County Council will approve and fund the contract agreed upon yesterday.

The current teachers contract expires June 30.