Chicago – As union and school board lawyers toiled in private here on Saturday to finish a contract that could soon lift the first teacher strike this city has seen in 25 years, a rally — not quite victory party, not quite vitriolic protest — was roaring just miles away.

Thousands of people, the largest celebration of union force since the strike began nearly a week ago, shook homemade protest signs in the air and wore the signature red T-shirts of the Chicago Teachers Union as they descended on Union Park, just west of downtown. The city skyline rose behind a stage from which a lineup of politicians, teachers, students and activists spoke about union strength and the need for better school conditions in the city.

Many in Chicago, home of the nation’s third-largest school system, began the weekend with renewed hope that the strike could soon end after news emerged on Friday that an outline of an agreement had been reached by negotiators. Still, many union supporters attending the rally on Saturday seemed uneasy about getting excited about the prospect of returning to work next week — and they were not yet ready to stop voicing their grievances about Mayor Rahm Emanuel’s education policies, which have been at the heart of these contentious negotiations.

“Until it’s signed on the line, we’re still going to fight,” said Julie Gabrick, a physical education teacher on the city’s Northwest Side. “We’re not going to give up that quick. We’ve been flexing our muscles all week and we’re going to keep at it until the bitter end.”

The weekend rally capped nearly a week of picketing at schools and marches that traversed the downtown streets. All the while, back-and-forth negotiations led to a series of mixed signals from the union and school board about how talks were progressing. Just days before, union officials described the two sides as “miles apart,” suggesting that the largest political crisis of Mr. Emanuel’s first mayoral term could drag on, even as parents dreaded the thought of another week of scrambling to find emergency child care.

But on Friday, leaders from both side of the dispute said the framework of an agreement had been reached. If negotiators can hash out the deal in writing this weekend, the union will most likely try to get approval from its nearly 800-delegate leadership body to lift the strike on Sunday. That could get students and teachers back into the classrooms by Monday, union officials said.

On Saturday, however, Karen Lewis, the president of the teachers union in Chicago, cautioned that the fight was not over until the deal was set writing. “We’re on strike,” she said in a speech, before returning to negotiations. “We have a framework for an agreement. We don’t have an agreement.”

While details of that framework were not made public, the conflict has largely centered around issues that included a longer school day, principals’ ability to hire teachers, a new teacher evaluation system and improving school conditions. The last proposal made public also suggested that raises for teachers — who make an average salary of about $75,000 a year, according to schools officials — could land somewhere around an average of 16 percent over four years.

The Saturday event, however, gave little attention to the deal being hashed out nearby. Instead, it celebrated the power of unions in Chicago and across the nation, which many here said have been under siege in recent years.

Billed as a “Wisconsin-style” event, in reference to the hundreds of thousands of people who flooded the streets in Madison last year to protest cuts in collective bargaining rights for most public workers, the gathering in Chicago drew hundreds of supporters from other states, including at least a half dozen busloads from Wisconsin and Minnesota.

“We had just been working toward these things in St. Paul and here they were erupting in Chicago,” said Mary Cathryn Ricker, the president of a teachers union in Minnesota who attended the Chicago rally, adding that workers across the country are watching this city’s negotiations closely.

Speaker after speaker, many from non-teacher unions — police, nurses, custodians — echoed that notion, proclaiming the power of organized labor and the need to stick together.

“You have proven to the world that you’re not going to take it anymore,” said Lorretta Johnson, secretary-treasurer of the American Federation of Teachers, in a speech to strikers, who later marched through Chicago streets, led by a high school marching band. “What you’ve done is send a message across this country and we heard it loud and clear.”