Leaders of striking teachers were optimistic yesterday about reopening schools Monday for 431,000 students idled by a 12-day walkout in the nation's third-largest school district.

"We're taking the necessary steps to settle the strike, hopefully by tomorrow, so that schools can open on Monday," Chicago Teachers Union President Jacqueline Vaughn said early yesterday after emerging from nine hours of talks. "We made progress today dealing with the key issues."

Vaughn said the teachers' union, the largest of 18 on strike, had reached agreement with the school board on all issues except "salary-related items and and makeup dates."

School board spokesman Robert Saigh said that, although a settlement appeared near, talks were being held up by the other striking organizations.

The nonteaching groups continued bargaining until 12:30 a.m. yesterday, trying to settle issues that the Board of Education claims are holding up a settlement of the district's second strike in 15 months.

Board member Frank Gardner said the 1,000-member maintenance workers' union is balking at changes in policies that he said would end "their outdated and unreasonable practice of denying minorities promotional opportunities."

Some 12,000 employes from 17 nonteaching unions walked off the job with the 28,000-member teachers' union on Dec. 3. All the labor groups must settle before the students will be back in school.