After more than 15 years arguing in courts that the city’s public schools are illegally under-funded, a long lawsuit that ended in 2006 in a victory, could the financial crisis and the budget cuts it’s causing pull education advocates back to court? Hard to imagine, but increasingly it does seem possible.

When I talked earlier this week to the Helaine Doran, the deputy director of the group that filed the lawsuit, the Campaign for Fiscal Equity, she was cautious about legal action. “We have no process of like, ‘Oh yes, we’re going back to court immediately,’” she said. “You have to look at the numbers and figure it out.” But there’s growing momentum suggesting court may be a possibility.

Michael Rebell’s editorial in the Daily News today uses stronger language. Rebell, a Columbia professor who was one of the lead attorneys in the original suit, calls Governor Paterson’s proposed budget, which would cut school funding below this school year’s level, “illegal” and “unconstitutional.” In a sign that he’s serious about follow-through, he also defines what wouldn’t be illegal: Maintaining an increase in funds, but slowing its rate. He says that option is troubling but “does not raise the same constitutional issues.”

Billy Easton, who is the executive director of the campaign’s Albany counterpart, the Alliance for Quality Education, is also making it clear that he thinks Governor Paterson’s budget isn’t just upsetting but illegal. He told me last night, “The increased school funding and the CFE funding is part of law. It’s not a promise. It’s a law pursuant to a court order.”