President Obama’s reelection campaign launched a national drive Friday to counter new restrictive voter-access laws, which advisers said threaten his electoral chances in November.

Organizers will fan out in key swing states this weekend to teach volunteers and voters how to navigate a series of laws passed by Republican-controlled state legislatures imposing stricter identification requirements, limiting early voting and making it harder to organize voter-registration drives.

It is the beginning of a months-long effort, campaign officials said, to combat what they described as a Republican effort to stifle voting among young people and minorities, two groups that traditionally tend to vote Democratic. . . .

The Obama campaign’s “weekend of action” is part of a field effort that in 2008 helped identify, register and turn out millions of new voters. Those new voters gave Obama wins in unlikely places, including North Carolina and Virginia, where young and minority voters helped make the difference. Turning out those voters again this year is key to the president’s reelection strategy, but it is also more challenging this year in part because of the new voting laws.