The nation's oldest and largest organization of Spanish-speaking citizens today elected a new president who is pledged to "ending the Hispanics' status as the country's invisible minority."

Ruben Bonilla, the new president of the 50,000-member League of United Latin American Citizens, defeated what he had called the "conservative, arrogant, middle-class old guard" of LULAC in unseating President Eduardo Pena.

Amid shouts of "Arriba con Bonilla," his supporters carried him to the convention platform on their shoulders after he received more than 60 percent of the convention's 500 delegate votes.

LULAC, which celebrated its 50th anniversary at the Houston convention, has chapters in 30 states. Although some Puerto Ricans and Cuban Americans are members, its greatest strength is among Mexican Americans.

Bonilla, 32, who as director of Texas LULAC has been an outspoken critic of alleged police brutality against Mexican Americans in his state, promised to "serve as an advocate for all Hispanic Americans."

A Corpus Christi, Tex., lawyer and a member of a politically powerful south Texas family, Bonilla said he hopes to make LULAC as politically influential on the nationl scene as the Urban League and the NAACP are for blacks.

Bonilla's well-organized election effort signaled a stunning departure from the low key LULAC conventions of past years.

His most enthusiastic supporters were delegates from small, impoverished towns in rural Texas. Often clad in T-shirts and blue jeans, they were in sharp contract to the urban and more fashionably dressed Pena supporters.

The pride they displayed in their heritage also contrasted with the traditional LULAC style of emphasizing assimilation into the American cultural mainstream.

Women supporters of Bonilla, for example, called themselves "Las Adelitas," a name taken from a Mexican anthem to the women who fought in the army of peasant revolutionary Emiliano Zapata.

Pena, a Washington, D.C., attorney and a former executive in the Equal Employment Opportunity Commission, called Bonilla's style "abrasive" and warned that it would "close doors that are open" with the Carter administration.

"I don't see any doors open," Bonilla replied.

Sarah Weddington, President Carter's adviser on women's issues, and Secretary of Labor Ray Marshall addressed the convention. Marshall said unemployment among Hispanics has dropped by about a third to 7.5 percent during the Carter administration.

However, two Republican presidential candidates who also spoke cited Carter's joke about "Montezuma's revenge" during his recent state visit to Mexico as evidence of his insensitivity to Latin American feelings.

Former United Nations ambassador George Bush called the reported remark "gratuitously offensive," while Los Angeles businessman Ben Fernandez said Carter's visit compared poorly with Cuban President Fidel Castro's recent Mexican trip.

Bonilla, who said he will preside over LULAC from Texas rather than from the organization's Washington office, said LULAC willseek greater Hispanic American voting strength through lawsuits against gerrymandered state and local election districts, and he urged the coalition of the black and Hispanic congressional caucuses.