WASHINGTON – Barack Obama won ugly. He lost most of the final contests. He lost key states by landslide margins, even after everyone besides Hillary Rodham Clinton agreed the race was over. He struggled to connect with blue-collar whites.

And – less talked about – he revealed a serious vulnerability with the fastest-growing part of the electorate, losing 2-1 among Hispanics in some places.

"The Hispanic community is one that cannot be taken for granted," said Rep. Henry Cuellar of Laredo, a Clinton supporter whose border district gave Mrs. Clinton more votes than any other in Texas' primary in March.

Mr. Obama, he said, needs to do "extensive outreach" to Hispanics, particularly Hispanic legislators, a key group the senator – like John Kerry in 2004 – has largely ignored.

Compared with Mrs. Clinton, Mr. Obama was an unknown quantity among Hispanics. There's a history of black-brown tension, still very much on the minds of older Hispanic voters. Part of it is his own relatively light experience and contacts with Latinos.

Mr. Obama had never even seen the Texas-Mexico border until a few days before the primary.

"I've been in Mexico when I was in college and was going to school in Southern California. I can't entirely talk about it," he joked after surveying the border at Brownsville.

Granted, he avoided the sort of faux pas that befell Gerald Ford, who bit into a tamale – husk and all – during a stop in San Antonio in 1976. But a level of ignorance did show through when Mr. Obama referred to his own time in "San Antone," and when, after sampling a torta at a Sombrero Festival in Brownsville, he described the delicacy as a "tosta."

All of which suggests a steep learning curve on issues of intense interest to Hispanics – a heterogeneous bloc that Sen. John McCain doesn't plan to cede.

The Arizona Republican may not attract the 40 percent to 45 percent President Bush got. But he won hearts over the years with his politically risky push for comprehensive immigration reform, including a path to citizenship for illegal immigrants. He distanced himself from that moderate image this year, assuring GOP hardliners that he'll tighten border security before seeking immigration reform again.

But activists see a battle grande brewing, especially in swing states such as New Mexico, Nevada, Colorado and Florida that have substantial Hispanic populations.

A recent Gallup Poll shows Mr. Obama leading 62-29 among Hispanic voters, though other surveys show a much tighter contest.

The Democrat is already getting help from New Mexico Gov. Bill Richardson and Federico Peña, the former Denver mayor and Cabinet secretary under Bill Clinton. Now that Mr. Obama has won, Mrs. Clinton's prominent Latino supporters are starting to come aboard.

Mr. Obama began wooing the Congressional Hispanic Caucus on Wednesday, placing a call to chairman Rep. Joe Baca, D-Calif.

"The older Latino voter is probably a little more set in their ways," said Rep. Charlie Gonzalez, D-San Antonio, one of the few Hispanic lawmakers to be an early Obama supporter. But now that Mrs. Clinton has given Mr. Obama her public blessing, he predicted, his colleagues will "campaign hard [and] it will mean a lot."

Mr. Gonzalez said Hispanic Clinton backers will like Mr. Obama once they give him a chance. But first, he said, Mr. Obama has to "make himself much better known in that community as to what his agenda is."