Barack Obama urged young American women to fight for their right to contraception and abortions, as Left-wing allies accused Mitt Romney of "throwing women under the bus" by seeking a crackdown.
Mr Obama's Democrats claim the Republicans are waging a "war on women" by attempting to crack down on their abortion rights and making it more difficult to obtain birth control
The US president told students graduating from an elite all-women's college in New York that they would face challenges to their equality in the workplace and to their right to "control your own health", noting that politicians were "relighting long-settled battles over women's rights".
"We are better off when women are treated fairly and equally in every respect, whether it is the salary you earn or the health decisions that you make," Mr Obama said at Barnard College. "Fight for your seat at the table, or better yet, fight for a seat at the head of the table."
His remarks threatened to reignite a row over the rights of women in modern America that his re-election campaign has tried to keep alive beyond the Republican party's presidential primary contest.
Mr Obama's Democrats claim the Republicans are waging a "war on women" by attempting to crack down on their abortion rights and making it more difficult to obtain birth control.
In a thinly-veiled attack on Mr Romney, Mr Obama said in his speech that "those who have opposed change" have lost in the past. "I believe they will lose this time as well," he said.
In becoming the presumed Republican presidential nominee, Mr Romney, once a relative moderate, took a series of strident positions including promising to "get rid of" Planned Parenthood, a network of women's health clinics. He favours overturning Roe vs. Wade, the historic Supreme Court decision granting the right to abortion, which he describes as "one of the darkest moments" in the court's history.
Opinion polls place Mr Obama as many as 14 percentage points ahead of Mr Romney among women, a deficit he must reduce drastically if he is to unseat the President in November.
An advertisement released on Monday by MoveOn.org, a Left-wing pressure group, pledged to remind voters how Mr Romney "threw women under the bus just to get the nomination" of his party.
They also focused on Mr Romney's pledge to scrap Mr Obama's overhaul of the health care system, which dictates that insurance packages provided for staff by bosses must include birth control.
"All you had to do was threaten to let our employers take away our contraception coverage, [and] threaten to let our insurance companies charge us more, just because we're women," its narrators said.
The Republicans dismissed Mr Obama's attacks, pointing out women had suffered disproportionately in the jobs market under his presidency and barely benefited in what they called a "hecovery".
"Obama won't mention that many college graduates will be unable to find a job thanks to his failed policies," a spokesman said.
Kate Christensen, a Barnard student and young Republican, described Mr Obama's decision to speak as "extremely political".
The college was "being used as a pawn in that makes me personally feel like he doesn't genuinely care about the praiseworthy and notable things Barnard is doing to make the world a better place,
Mr Obama was given the speaking role after Rush Limbaugh, an influential Right-wing radio host, described Sandra Fluke, a graduate student campaigning for subsidised contraception, as a "slut".