“We are here today to tell you that we stand with you,” Mr. Cuomo said. “You are not alone. We will save charter schools.”

Mr. de Blasio has pledged to slow the growth of charter schools in New York City, and announced last week that he would block three schools from using space in traditional public school buildings. The move was denounced by charter school leaders, who promised to show up en masse in the state capital to voice their dissent.

Mr. de Blasio, who also traveled to Albany on Tuesday to once again press for a tax on the city’s wealthiest residents to pay for universal prekindergarten, last week dismissed their efforts as a “sideshow.”

Mr. Cuomo’s decision to speak at the rally brought the issue center stage, sapping some of the attention from Mr. de Blasio’s rally, and set up yet another political battle between the new mayor and the governor — one that might have wider national implications since the efficacy of charter schools is a subject of debate across the country.