CHICAGO, SEPT. 8 -- Public school teachers, deadlocked in salary negotiations with the city school board, went on strike here today for the ninth time in 18 years.

The Chicago Teachers Union set up pickets at schools and school administration offices after marathon Labor Day weekend bargaining sessions failed to resolve the dispute in the nation's third-largest school system.

Delayed school openings have become a chronic problem here and in other large urban districts as increasingly strong unions have sought wage hikes.

Teachers also are on strike today in Detroit, in five other Michigan districts, seven Pennyslvania districts and districts in Ohio, New Jersey and Washington state. Negotiations here were scheduled to resume tonight, but officials held out little hope of a quick settlement, and many here predict a prolonged strike.

Mayor Harold Washington (D) urged both sides to stay at the bargaining table and extend their contract until the state legislature meets in October.

"My position is we don't want the schools closed," he said at a news conference, but he was not optimistic.

"The stark reality is the parties are rather rigid," the mayor said.

The union, representing 29,000 teachers, is seeking a two-year contract with a 10 percent raise this year and a 5 percent raise next year. The Chicago Board of Education has offered a 1.7 percent pay cut in the form of three new unpaid days off for each teacher.

Teachers were to have reported for work today with classes for 430,000 students at 594 schools beginning Wednesday.

This is the ninth strike here since 1969. A typical Chicago high school senior has missed 49 days of classes due to strikes -- 11 days in kindergarten, 10 in fifth grade, 16 in eighth grade, 10 in ninth grade and two in 10th grade. Some days were made up in summer.

Earlier strikes were resolved when the mayor or the governor came to the rescue. This year, Washington and Illinois Gov. James R. Thompson (R) insist that will not happen. Each claims the strike is not his problem.

Although all 11 members of the Board of Education are his appointees, Washington has refused to mediate. "The pressure point is the state legislature and the governor. It's not here," he said today.

Later, he added, "We don't have any money. So why should I call people in here to ying-yang them around and make it appear there is progress when there isn't any?"

Thompson proposed major tax increases this year, directed in part at increasing state aid to education. But his proposals were rejected by the state legislature.

"Illinois came up very short when the state chose not to raise taxes," said University of Illinois economist Fred Giertz, an authority on state finance.

"The situation is you have a powerful union in Chicago. Teachers have heard a lot of talk about education reform the last few years and not much money behind it. They view the union as one avenue to advancement."

The average Chicago school teacher earns $32,011, including pension benefits, under the current contract.

Beginning teachers receive $17,651; the top salary for a teacher with 15 years experience and a doctorate is $37,517.

The rates are below those of wealthier suburban districts in the Chicago area.

The school board's $1.8 billion budget provides for an average 3 percent automatic raise for teachers with less than 15 years experience. Fewer than half the teachers fall in this category, however.

The board estimates that the union request would cost $150 million.

{School board spokesman Bob Saigh said school lawyers had asked the Illinois Educational Labor Relations Board to issue an unfair labor practice complaint against the teachers union and other employe unions honoring the strike, Associated Press reported.}

In Detroit, 12,000 teachers have been on strike since Aug. 31, idling 193,000 students. The school district says its $27 million deficit makes it unable to meet the union's demand for a 14 percent increase.