CHICAGO, OCT. 3 -- Negotiators for striking teachers and the Board of Education reached a tentative agreement today on a new contract that includes pay raises but also 1,800 layoffs, ending a record walkout that forced 430,000 students to miss 18 days of school.

The settlement in the nation's third-largest school district came amid mounting public pressure from community groups and parents, who vowed to open schools on their own if there was no agreement by Monday.

"The school strike is over. The school doors will be open on Monday, and our children soon will be back at their desks," Mayor Harold Washington (D) said at an afternoon news conference.

The strike by the 29,000-member Chicago Teachers Union and 12,000 other union employes began Sept. 8, lasted 26 days and was the longest in the city's history.

Union officials said they expected teachers to ratify the two-year contract Sunday night. Teachers were expected back in schools Monday for preparatory work, and classes were scheduled to begin Tuesday.

The two-year pact contains a pay raise of 4 percent in the first year and a 4 percent raise the second year, which is contingent upon the availability of additional funding from the state. The contract also calls for a reduction in class size at 100 schools with under-achieving students.

Schools Superintendent Manford Byrd said the new contract will result in about 1,800 layoffs "all over the system." He said 500 to 600 employes will receive notices as early as Monday or Tuesday.

Counseling programs will be affected, there will be a reduction of the number of assistant principals and some special education services will be eliminated, Byrd said.

CTU President Jacqueline Vaughn said she will tell her membership that the new contract is a good compromise.

"I will tell them that their efforts were not in vain," Vaughn said. "We did not get what we had hoped to get . . . {but} this is a good first step."

Teachers remain on strike in Pennsylvania, New Jersey and Arkansas, idling some 45,000 students.