What began as a routine drunken-driving arrest in Texas last year is turning into an important civil rights test case for Mexican Americans.

The controversy stems from long-standing claims that many police officers in southwestern states frequently arrest chicanos and hold them as illegal immigrants.

The case involves Gerardo Rivera, 22, a factory worker, U.S. citizen and Dallas resident who filed a $5.4 million federal class-action suit against the city of Grand Prairie.

Filed last July in Dallas, the suit alleges that Rivea and a companion, Ruben Palacios, were arrested Sept. 2, 1978, on speeding and drunken-driving charges, taken to the Grand Prairie jail and held nearly two days without legal counsel on grounds that they could not prove U.S. citizenship.

Rivera eventually proved his citizenship. Palacios, an illegal immigrant, could not. Rivera sued. Palacios disappeared after being released from jail.

The Rivera suit is attracting the attention of Mexican-American and other civil rights lawyers in the West and Southwest who say the Grand Prairie incident is symptomatic of widespread abuse of chicano citizens who frequently are mistaken for undocumented illegal Mexican immigrants.

The San Francisco-based Mexican-Amerian Legal Defense and Educational Fund (MALDEF), which has built a reputation arguing chicano rights cases, has joined Rivera's Dallas lawyers in the suit.

"This problem of picking up Mexican-American citizens just because they look like so-called illegal aliens is really getting serious," said Al Perez, MALDEF associate counsel.

"It seems that with all of the attention the media has been giving to undocumented workers, a lot of policemen are making themselves exofficio members of the U.S. Immigration and Naturalization Service. We want to try to terminate that practice with this suit," Perez said.

William F. Callejo, one of Rivera's Dallas lawyers, put it this way: "Obviously, if we win in Dallas, that one decision isn't going to be binding on all juridictions. But a multimillion-dollar victory against Grand Prairie will make other people stop and think before they hold some other chicano in jail because he looks illegal."

Officials in Grand Prairie, a Dallas suburb, say the suit is unfair and illconceived.

"We've got one of the most respected police forces in this area," said City Manager Cliff Johnson, who is one of the defendants. We certainly have confidence in our policemen and we don't think it's fair to try to hang a thing like this on them.

Johnson said Grand Prairie police records show that the arresting officer, Billy Bob Ballard, acted properly and that Rivera and Palacios were treated fairly once incarcerated.

"The patrolman stopped the Rivera car for speeding," Johnson said. "When Rivera got out of the car, he fell down. He was drunk.

"He had $14.10 cash on his person . . . . His bail bond was set at $200. He stayed in the city jail until his lawyer, Mr. Callejo, made an appearance with necessary bond.

"Mr. Rivera was not arrested because he was a suspected illegal. He was arrested because he was speeding, driving and drunk, and that's that," Johnson said.

Johnson said, I think these people are filing a suit over the wrong person." He gave no details on Palacios.

Civil rights lawyers familiar with the life of chicanos in the Southwest, particularly in largely working-class Grand Prairie, tell a different story. Allegations contained in the Rivera suit portray daily events, they say.

"There's no question in my mind that police officials in Grand Prairie routinely pick up chicano citizens on traffic charges and sometimes no charges at all, and hold them on suspicion of having entered the country illegally," said civil rights lawyer Warren Burnett of Odessa, Tex.

"The thing is that local police officials have no authority, no business, arresting people on suspicion of illegal entry. That's a job for the INS. But in Grand Prairie, where you have a lot of illegal immigrants working in the service industries, local policemen pick up chicano citizens every day and hold them on suspicion of being illegal," Burnett said.

The Rivera suit alleges that Patrolman Ballard "disparagingly called Rivera a 'wetback' and insisted that he was a 'wetback' upon making the arrest.

Though Rivera told the officer he was a U.S. citizen, both he and Palacios were taken to jail, were denied representation though their "attorney stood ready and would have obtained their immediate release," and were ordered "held for investigation of illegal entry."

The attorney, Callejo, said Grand Prairie police prevented him from going to the immediate aid of his client because Rivera could not prove he was a citizen.

"You can't do that to a Greek American or an Italian American who is arrested on a traffic charge. You shouldn't be able to do it to a Mexican American, either," Callejo said.