On a recent summer's day, Sandra Cisneros walked into Valenzuela's Latino Bookstore and thought she had discovered a treasure. It was one of the few independent book sellers in her home town of San Antonio, and on top of that, she said, its name appealed directly to her.

But within minutes, her mood changed. A clerk innocently used a word to describe a section of books that made Cisneros's skin crawl. "She used the word Hispanic," Cisneros said, her voice dripping with indignation. "I wanted to ask her, 'Why are you using that word?'

"People who use that word don't know why they're using it," said Cisneros, a Mexican American poet and novelist. "To me, it's like a slave name. I'm a Latina."

That declaration -- "I'm a Latina" -- is resounding more and more through the vast and diverse Spanish-speaking population that dethroned African Americans as the nation's largest ethnic group a few months ago.

It is also deepening a somewhat hidden but contentious debate over how the group should identify itself -- as Hispanics or Latinos. The debate is increasingly popping up wherever Spanish speakers gather.

It was raised last month at the National Council of La Raza's convention in Austin. The Internet is littered with articles and position papers on the issue. Civic organizations with Hispanic in their titles have withstood revolts by activist members seeking to replace it with the word Latino.

Cisneros refused to appear on the cover of Hispanic magazine earlier this year because of its name. She relented only after editors allowed her to wear a huge faux tattoo on her biceps that read "Pura Latina," or Pure Latina.

Another Mexican American writer, Luis J. Rodriguez, only reluctantly accepted an award from a Hispanic organization "because I'm not Hispanic," he said.

Some have called the argument an insignificant disagreement over words that is being blown out of proportion. But others believe such labels can change the course of a people, as advocates of "black power" showed when they cast aside the term Negro during their crusade for self-determination amid the 1960s civil rights movement.

"I think the debate reflects the flux this community is in right now," said Angelo Falcon, a senior policy executive for the Puerto Rican Legal and Education Fund. "It's almost like a story where you ask, 'Where might this community be going?' "

Although the terms Latino and Hispanic have been used interchangeably for decades, experts who have studied their meanings say the words trace the original bloodlines of Spanish speakers to different populations in opposite parts of the world.

Hispanics derive from the mostly white Iberian peninsula that includes Spain and Portugal, while Latinos are descended from the brown indigenous Indians of the Americas south of the United States and in the Caribbean, conquered by Spain centuries ago.

Latino-Hispanic is an ethnic category in which people can be of any race. They are white, like the Mexican American boxer Oscar de la Hoya, and black, like the Dominican baseball slugger Sammy Sosa.

They can also be Ameri-Indian and Asian. A great many are mixtures of several races. More than 90 percent of those who said they are of "some other race" on the 2000 Census identified themselves as Hispanic or Latino.

"As a poet, I'm especially sensitive to the power a word has," said Cisneros, who wrote the books "Caramelo" and "The House on Mango Street." "It's not a word. It's a way of looking at the world. It's a way of looking at meaning."

Duard Bradshaw has a different opinion. "I'll tell you why I like the word Hispanic," said the Panamanian president of the Hispanic National Bar Association. "If we use the word Latino, it excludes the Iberian peninsula and the Spaniards. The Iberian peninsula is where we came from. We all have that little thread that's from Spain."

A survey of the community conducted last year by the Pew Hispanic Center of Washington found that nearly all people from Spanish-speaking backgrounds identify themselves primarily by their place of national origin.

When asked to describe the wider community, more than half, 53 percent, said both Hispanic and Latino define them. A substantial but smaller group, 34 percent, favored the term Hispanic. The smallest group, 13 percent, said they preferred Latino. A survey by Hispanic Trends magazine produced a similar finding.

But advocates for the term Latino were unfazed.

"The very fact that it's called the Pew Hispanic Center tells you something," said Fernando Guerra, the Mexican American director of the Center for the Study of Los Angeles at Loyola Marymount University. "The fact that Hispanic is in the name of the organization . . . biased the question."

The term Hispanic was given prominence by the Nixon administration more than 30 years ago when it was added to the census questionnaire in 1970. Although that year's count of the large Mexican American, Puerto Rican and Cuban American populations was a disappointment, a seed had been planted.

By the 1980 Census, Hispanic had become fixed as the official government term. It appeared not only on census forms, but also on all other federal, state and municipal applications for employment, general assistance and school enrollment.

"It's a great gift that the government of the United States gave us," said Vincent Pinzon, the Colombian president and founder of the Americas Foundation. "If you want to acquire political muscle in this country, and you say you're just Argentinian or Colombian, then you have none."

But Mexican American activists in California and Puerto Rican activists in New York were not pleased. They favored a term that included the brown indigenous Indians who they believe are the source of their bloodline.

"Hispanic doesn't work for me because it's about people from Spain," said Rodriguez, author of the book "The Republic of East L.A." "I'm Mexican, and we were conquered by people from Spain, so it's kind of an insult."

Rodriguez's views are typical of Mexican Americans in Los Angeles, the epicenter of immigrants from that country, and the Chicano rights movement.

The term Chicano is thought to have originated as slang that described immigrants and refugees from the Mexican revolution. The term later evolved to define the uprising of Mexican American reformers and rights activists as well as farm laborers and other workers who lived in squalor while toiling for low pay.

As activists from other Latin countries joined the movement, Latino was adopted as an umbrella term for all groups.

"In L.A., if someone says he's Hispanic, and he's not from the East Coast, you begin to question this guy," said Guerra, the Loyola Marymount professor. "It means he didn't grow up in a Latino neighborhood."

In Washington, where the Pew Center is located, Salvadorans who dominate the area's large Central American population say "somos Latinos" -- we are Latinos -- according to Jose Ramos, director of the United Salvadoran American Civic Committee.

"Hispanic is a category for the U.S. Census," he said. "It's a formality. For me, the correct term is Latino. It identifies people who speak the same language, people who share a vision of the historical meaning of our community. I am Salvadoran, and I am Latino."

But Cuban immigrants in Miami, conservative Mexican Americans in Texas and a group of Spanish descendants in New Mexico are among the groups that strongly identify themselves as Hispanic.

The word Latin dates to an 18th century spat between England and France, according to a historical resource guide written by journalist Frank del Olmo for the National Association of Hispanic Journalists.

Latin was used to distinguish Italy, France, Spain and their conquered territories in the Americas from the British empire and its colonies. Latino was popularized during the social movements of the 1960s, Guerra and other historians said.

The disagreement over the pair of ancient terms is an annoyance to some. When the subject came up at the National Council of La Raza's annual meeting, Lisa Navarette, the group's Cuban American spokeswoman, dismissed it. "We've got so many real important issues to work on, we can't be bothered with this nit-picking."

The community indeed faces daunting challenges: high unemployment, a skyrocketing high school dropout rate, widespread opposition to immigration reform and crowded communities.

But the issue isn't apt to disappear. A few years ago, Bradshaw's group, the Hispanic National Bar Association in Washington, had to fight off a resolution by a group of members to remove the word Hispanic from its name and replace it with Latino.

Last semester, students at Southern Methodist University in Dallas talked about changing the name Hispanic Student Services. And earlier this year, Cisneros, the author who abhors the word Hispanic, refused to accept an award from a Hispanic organization.

At the Latino bookstore Cisneros visited, owner Richard Martinez didn't know what to think. "I don't know which is correct," he said. "I'm a Mexican, a Latino, a Hispanic, whatever. Be who you are. Be proud, like everyone else."

Sandra Cisneros, a novelist and poet, rejects the term "Hispanic." "To me, it's like a slave name," she says. "I'm a Latina."