SAN DIEGO | Sen. Barack Obama received a rock-star welcome Sunday from the nation's largest Hispanic rights group, telling them they are the critical swing group in November's presidential election and promising a renewed effort to pass an immigration bill during his first year in office.

"This election is nothing less than a test of our allegiance to the American dream," the Democrats' presumptive presidential nominee told the National Council of La Raza (NCLR) convention, in a speech in which he also proposed a tax credit to help small businesses pay for health insurance for their employees.

Getty Images Thalia Mendoza poses with cardboard images of Sens. Barack Obama and John McCain at the convention of the National Council of La Raza, a large Hispanic rights group that is hosting speeches by both presidential candidates this week in San Diego.

Janet Murguia, president and chief executive of NCLR, heaped praise on Mr. Obama for both his leadership on immigration and his personal outreach to NCLR. It was a boon for the senator from Illinois, who is sparring with presidential opponent Sen. John McCain, Arizona Republican, over who accomplished more on last year's immigration bill.

She said Mr. Obama "stood with us" in the immigration fight, and said Mr. Obama also has made strong efforts to court Hispanic leaders, telling the convention that Mr. Obama personally sought out NCLR in 2005 and visited Ms. Murguia at NCLR's office soon after he was sworn in as senator.

"What stuck with me was that a newly elected U.S. senator came to us, to our home. That had never, ever happened before, or since for that matter," she said.

Mr. McCain's campaign has tried to drive a wedge between Mr. Obama and Hispanic voters, arguing that the Democrat worked against the 2007 bill by voting to halve the number of future immigrant workers that would be allowed.

Rosario Marin, a U.S. treasurer during President Bush's first term, said the bill was killed by "people like Senator Obama casting votes that eventually unraveled the immigration package that [Mr. McCain] had so carefully put together."

That bill was defeated when a majority of senators, including 15 Democrats, voted to filibuster it. Both Mr. McCain and Mr. Obama voted against the filibuster.

Mr. McCain was the author of a 2006 bill that was the precursor to last year's measure, but now says the government must prove it can secure the borders first as part of any immigration bill. Since the 2007 bill's failure, Mr. McCain has sponsored and supported several enforcement-first measures, and on Sunday his top domestic policy adviser, Douglas J. Holtz-Eakin, said Mr. McCain, as president, could take steps to secure the border without the approval of Congress.

"They require no new legislation, the money is there, the authority is there," Mr. Holtz-Eakin said.

Mr. McCain has said his goal is to have border-state governors certify that the U.S.-Mexico boundary is secure before moving to the broader immigration issue.

Brian Rogers, a campaign spokesman, said Mr. McCain's support for $3 billion in border security funding and his co-sponsorship of an enforcement-only bill along with Republican Sens. Jon Kyl of Arizona, Jeff Sessions of Alabama, John Cornyn of Texas and Lindsey Graham of South Carolina last August demonstrate his priorities. That bill never passed.

"Should existing appropriations and budget authority prove insufficient to secure our borders to meet the standards of certification he has articulated, John McCain would pursue further legislation to assure his commitment is kept," Mr. Rogers said.

Several attendees at NCLR's convention said Mr. McCain will have a difficult time trying to appeal to both Hispanic voters and conservatives who want to see stricter border enforcement.

In Sunday's speech, Mr. Obama said that by embracing the "enforcement-first" approach, Mr. McCain has now in effect "abandoned his courageous stance" he took to support last year's bill.

Speaking last month to another Hispanic group, the National Association of Latino Elected and Appointed Officials, Mr. McCain backed away from another part of last year's immigration bill by embracing a temporary worker program for future foreign workers. Last year's bill called for future guest workers to have an opportunity to apply for legal permanent residence, putting them on the path to citizenship.

Both men have work to do to woo Hispanic voters. Mr. Obama's former presidential nomination opponent, Sen. Hillary Rodham Clinton of New York, dominated among Hispanics in the primaries, and Hispanics turned out in far greater numbers in the Democratic contests.

But judging from his reception Sunday, Mr. Obama is making inroads. As the doors to the convention center room opened, dozens of attendees, particularly young women, rushed the room to get the best possible views of the podium for the senator's speech.

Trying to cloak himself in Mrs. Clinton's appeal, Mr. Obama told NCLR he was adjusting his health care plan to adopt a business tax credit proposal that was part of Mrs. Clinton's plan. He did not go into detail, but said it would help small businesses without imposing "any new burdens."

In a memo, his campaign said the plan would allow a refundable credit of up to 50 percent of the premiums that small businesses pay for their employees' health care. The plan, which would cost $6 billion a year, would be less generous for larger companies with high-income employees.

Hispanics account for a substantial portion of small-business creation.

Republicans said Mr. Obama was tweaking his health care plan because some Democrats said it could hurt small businesses.

"This is an obvious and crude effort to spackle together a quick political fix, but it lacks specifics, lacks funding and he lacks credibility," said Tucker Bounds, a McCain campaign spokesman.