WASHINGTON (Reuters) - President Barack Obama told Hispanic voters on Thursday he was ready to sign a broad-based immigration fix, blaming his political rivals in Washington for blocking one of his major unmet campaign promises from 2008.

At a Cinco de Mayo reception he hosted at the White House, Obama he would keep fighting for reforms to grant children of undocumented workers a path to U.S. citizenship and address other problems with the country's complex immigration rules.

"'No' is not an option. I want to sign the DREAM Act into law. I've got the pens all ready," he told the Rose Garden event featuring margaritas and tacos held two days ahead of May 5, marked in the United States to celebrate Mexican culture.

"I'm willing to work with anybody who is serious to get this done and to achieve bipartisan comprehensive immigration reform to solve this challenge once and for all," he said.

Latino voters could be pivotal in the race for the White House on November 6, particularly in battleground states like Florida, Arizona, Colorado and Virginia.

Obama, a Democrat, is polling ahead among Hispanics of the likely Republican contender Mitt Romney. But many Latinos are disappointed the president failed to deliver immigration reform so far and are upset about the high deportation numbers on his watch.

Last month, the president said he would tackle immigration reform right away in his second term if re-elected.

(Reporting By Samson Reiny)