DENVER — President Obama made one of his strongest pitches to date for the women’s vote, which is crucial to his re-election, telling a mostly female crowd of 4,000 here on Wednesday that Republicans led by Mitt Romney would take them back to the era of the 1950s.

Mr. Romney, who was in Colorado last week, on Wednesday was in another swing state, Iowa, which Mr. Obama will tour by bus next week. Their itineraries underscored the push to mobilize supporters and win over the few undecided voters in the relatively few battleground states that will decide the election.

In Des Moines, Mr. Romney called for developing a range of energy resources including wind power, but he pointedly did not mention his opposition to an administration-supported tax credit for the wind industry that Republican leaders in both Iowa and Colorado strongly favor. Iowa Republicans, including Gov. Terry E. Branstad, have publicly criticized Mr. Romney for his stance. And in Colorado, Mr. Obama is stoking the controversy during his two-day, four-stop visit.

But at his first stop at a Denver campus shared by three colleges, Mr. Obama’s emphasis was on women’s health and reproductive issues. He was introduced by Sandra Fluke, the Georgetown Law School graduate who this year became a hero to women’s groups, and the target of conservatives like Rush Limbaugh, who called her “a prostitute,” after Republicans blocked her from testifying in Congress for insurance coverage of contraception.