A federal judge on Thursday blocked key provisions of a ­Florida law regulating groups that organize voter-registration drives, escalating a debate over newly restrictive voter-access laws that have become a major issue in the presidential campaign.

The decision by U.S. District Judge Robert L. Hinkle marked the first time a federal jurist has struck down provisions in one of the voting laws passed by nearly 20 states since last year. The laws are a flashpoint in President Obama’s battle for reelection, with his supporters saying they target minorities and other pro-Obama groups. Republicans say the measures are needed to combat voter fraud.

In Tallahassee, Hinkle blocked Florida from enforcing parts of its new voting law, including provisions that require groups that collect voter registration forms to return them to state officials within 48 hours. The provisions also mandate that all volunteer workers must file sworn statements saying they will obey state laws in registering voters.

The judge called the 48-hour deadline “harsh and impractical” and said the sworn statement “could have no purpose other than to discourage voluntary participation in legitimate, indeed constitutionally protected, activities.’’

“An election-code provision . . . must serve a legitimate purpose that is sufficient to warrant the burden it imposes on the right to vote,’’ Hinkle wrote in granting a preliminary injunction blocking the provisions. Other parts of the law remain intact, including one that requires voter-registration organizations to “pre-register” with the state before enaging in voter-registration drives.

The Obama campaign and lawyers for the New York-based Brennan Center for Justice, which challenged the law on behalf of three groups that register Florida voters, hailed the decision. “This ruling is a significant victory . . . for the voters of Florida and for the constitutional right to engage with fellow citizens and ultimately to help people get on the voter rolls,’’ said Lee Rowland, who argued the case for the center.

John Lucas, a spokesman for Florida Attorney General Pam Bondi, said the office is reviewing the ruling and declined to say if the state will appeal. Florida Gov. Rick Scott (R) in May 2011 signed the legislation, part of a wave of state laws regulating how people can vote.

The laws have drawn strong opposition from civil rights and other groups, which argue that they are designed to stifle voting among young people and minorities, who tend to vote Democratic. Republicans say they are needed to make elections fairer and accuse the Obama adminstration of opposing the measures to further the president’s reelection prospects.

The battle has focused mostly on the nine states that passed laws requiring voters to show photo identification at the polls. A state judge has ruled Wisconsin’s voter identification law unconstitutional, and the Justice Department has blocked such laws in Texas and South Carolina. The department acted under the Voting Rights Act, which requires some states or counties with a history of discrimination to receive federal approval before changing their voting laws.

Five Florida counties are subject to that provision, and a separate legal battle is underway in federal court in the District over whether to approve provisions of the state law in those counties.