A Santa Clara County Superior Court judge ruled in favor of the new 49ers stadium and its backers Monday, paving the way for construction to begin as early as spring, according to the Santa Clara city attorney.

The ruling by Judge Peter Kirwan blocks opposition efforts to put the project back on the ballot. Voters initially approved the project with Measure J in June 2010.

Opponents of the project argue that the $850 million bank loan for the stadium would burden the residents and bankrupt the city.

Santa Clara Plays Fair, a group opposing the stadium project, led a campaign to collect more than 5,000 valid signatures to put the project back on the ballot.

The council authorized City Attorney Ren Nosky to file legal action in court and papers were filed several weeks ago, Nosky said.

City and stadium officials can now move forward with taking steps toward financing the stadium and beginning construction, he said.

"We're happy with the ruling," Nosky said.

Nosky said construction on the 68,000-seat stadium next to Great America theme park is expected to begin by spring or early summer this year.

A spokesman for Santa Clara Plays Fair was not immediately available for comment.