Montgomery County public school teachers, service employes and officials, unable to reach an agreement in contract talks, have called in mediators.

The action, announced after State School Superintendent David Hornbeck declared the groups had reached an impasse in their efforts to agree on a contract for next year, indicates that the talks, scheduled to resume this weekend, could be more rancorous and drawn out than past negotiations.

Some observers predict that school system administrators, fresh from a victory in contract talks with the supervisory personnel union, will be equally tough this time around and hold out for similar concessions from the remaining two unions: the Montgomery County Council of Supporting Services Employees, which represents 5,730 of the system's library aides, clerks, cafeteria workers and building technicians, and the Montgomery County Education Association, which represents the schools' 6,170 teachers.

In addition, county budget administrators are expected to monitor the talks carefully. Earlier this month Superintendent Edward Andrews proposed a $338 million school budget for next year but he did not include funds for salary increases in the figure.

According to school estimates, Andrews' proposed budget figure could rise by as much as $2.7 million for every percentage point of salary increase conceded by the administrators and approved by the school board. Using last year's salary increase of 9.5 percent as a guideline, a similar rise could cost the school system an additional $25.7 million, for a total budget figure of more than $363 million.

The County Council has urged the school system not to set a budget figure higher than about $352 million.

Representatives of the teachers and service employes unions are expected to ask for a raise at least equal to the annual cost-of-living increase, set this year at roughly 8 to 9 percent.

But the recent contract settlement with the Montgomery County Association of Administrative and Supervisory Personnel could indicate that the two unions may face a tough battle. The union, which represents principals and administrative supervisors, won a three-year contract with a 6 percent increase the first year and 5 percent, or three-quarters of the Consumer Price Index, whichever is lower, for each of following two years. The two sides agreed not to discuss specifics but sources close to the negotiations said the union initially asked for a nearly 15 percent salary hike.

Teachers union representative Walt Rogowski, who has been participating in contract talks, said he has told the negotiator that the terms of the supervisors union contract were "totally unacceptable" for the teachers.

The supervisors' three-year agreement, which was ratified Monday night by the union's 416 members, represents a departure from recent contracts in both the wage increase and length of contract. Two years ago, when the last contract was signed, school employe groups signed a two-year agreement for a 10 percent increase the first year and a 9.5 percent increase last year. Union representatives say the optimal agreement would have terms set only for one year.

It was the first time the administrators and supervisors' group tried to hammer out a contract with school officials after breaking off from the teachers union last year and forming its own union. The teachers union and support services union are negotiating separately with school officials.

If the two groups, with the help of mediators, are unable to reach an agreement in 10 days, the mediators will submit a report with recommendations. The school system and the unions are not obligated to accept the mediators' recommendations; a rejection would restart the negotiating process.

In addition to wages, major points of contention for the teachers union include employe benefits, compensation for participating in extracurricular activities and strike regulations.

Discussion of strike guidelines may be one of the more vitriolic topics at the bargaining table. The current contract does not contain language regarding strikes, but sources say school officials would like to include regulations prohibiting strikes in next year's agreement. Union and school representatives have agreed not to discuss the specifics of the talks, but the sources say teacher representatives are sure to oppose this proposal, arguing that state laws are stringent enough.

Teacher union representative Rogowski calls Maryland bargaining laws for public employes some of the toughest in the nation. Under state law, a teachers union is automatically decertified if its members go out on strike. Although the teachers would not be fired, they would have no unified representation.

Rogowski also expects employe benefits to be hotly debated, with the teachers union arguing that too much money is deducted from its members' paychecks to pay for insurance coverage. Teachers currently pay for insurance on a sliding scale, under which teachers with less experience pay for half the policy, while teachers who have taught 12 or more years in the county system pay only 15 percent.

Although cost of living increases will be a major part of the support services union demands, job security will probably be equally, if not more, important, said union representative Vincent Foo.

"Job security is very important to our people now with the economic situation in our country," said Foo, who expects the superintendent's proposed budget to eliminate 187 of his members' jobs. Unlike members of the teachers union, support service members are paid hourly, and this fact, says Foo, will factor strongly in discussions of the number of official school calendar days. According to Foo, school officials are considering cutting back the current calendar year from 185 days to 180.

"The proposal wouldn't hurt teachers who are paid annually, but some of our people could lose a week's pay," said Foo.

County Executive Charles W. Gilchrist has set a March 1 deadline for the school board to approve the budget and a May 15 date for the County Council to okay it, but union representatives said they would not be bound to those dates.

"As far as I'm concerned," said Rogowski, "I've always looked at the last possible day of bargaining as the opening day of school in fall.

"We simply can't bow to the pressure of an artificial date," he said.