By Tim Gaynor and David Schwartz

PHOENIX (Reuters) - Arizona lawman Joe Arpaio violated the constitutional rights of Latino drivers in his crackdown on illegal immigration, a federal judge found on Friday, and ordered him to stop using race as a factor in law enforcement decisions.

The ruling against the Maricopa County sheriff came in response to a class-action lawsuit brought by Hispanic drivers that tested whether police can target illegal immigrants without racially profiling U.S. citizens and legal residents of Hispanic origin.

U.S. District Court Judge Murray Snow ruled that the sheriff's policies violated the drivers' constitutional rights and ordered Arpaio's office to cease using race or ancestry as a grounds to stop, detain or hold occupants of vehicles - some of them in crime sweeps dubbed "saturation patrols."

"The great weight of the evidence is that all types of saturation patrols at issue in this case incorporated race as a consideration into their operations," Snow said in a written ruling.

He added that race had factored into which vehicles the deputies decided to stop, and into who they decided to investigate for immigration violations.

The lawsuit contended that Arpaio, who styles himself "America's toughest sheriff," and his officers violated the constitutional rights of both U.S. citizens and legal immigrants alike in their zeal to crack down on people they believe to be in the country illegally.

The ruling came days after a U.S. Senate panel approved a landmark comprehensive immigration legislation that would usher in the biggest changes in immigration policy in a generation if passed by Congress.

The bill would put 11 million immigrants without legal status on a 13-year path to citizenship while further strengthening security along the porous southwestern border with Mexico.

Arpaio declined to comment on the ruling. An attorney representing the sheriff's office said his clients were "deeply disappointed by the ruling" and would lodge an appeal.

"The Maricopa County Sheriff's Office has always held the position that they never have used race and never will use race in making a law enforcement decision," attorney Tim Casey told Reuters.

"We do disagree with the findings and my clients do intend to appeal, but at the same time ... we will work with the court and with the opposing counsel to comply fully with the letter and the spirit of this order," he added.

'ILLEGAL AND PLAIN UN-AMERICAN'

Cecillia Wang, director of the American Civil Liberties Union Immigrants' Rights Project and plaintiffs' counsel, called the judge's ruling "an important victory that will resound far beyond Maricopa County."

"Singling people out for traffic stops and detentions simply because they're Latino is illegal and just plain un-American," Wang said after the ruling was made public.

"Let this be a warning to anyone who hides behind a badge to wage their own private campaign against Latinos or immigrants that there is no exception in the Constitution for violating people's rights in immigration enforcement."

During testimony in the non-jury trial last year, Arpaio said he was against racial profiling and denied his office arrested people because of the color of their skin.

The sheriff, who won re-election to a sixth term in November, has been a lightning rod for controversy over his aggressive enforcement of immigration laws in the state, which borders Mexico, as well as an investigation into the validity of President Barack Obama's U.S. birth certificate.

The lawsuit was brought against Arpaio and his office on behalf of five Hispanic drivers who said they had been stopped by deputies because of their ethnicity.

The plaintiffs, which include the Somos America immigrants' rights coalition and all Latino drivers stopped by the sheriff's office since 2007, were seeking corrective action but not monetary damages.

Arpaio has been the subject of other probes and lawsuits. In August, the U.S. Attorney's Office in Arizona said it had closed a criminal investigation into accusations of financial misconduct by Arpaio, and it declined to bring charges.

A separate U.S. Justice Department investigation and lawsuit relating to accusations of civil rights abuses by Arpaio's office is ongoing.

Arizona has been at the heart of a bitter national debate over immigration since Republican Governor Jan Brewer signed a 2010 crackdown on illegal immigration.

The federal government challenged the crackdown in court and said the U.S. Constitution gives it sole authority over immigration policy. The U.S. Supreme Court, however, has allowed to stand the part of the law permitting police to question people they stop about their immigration status.

Snow scheduled a hearing in the case for June 14 at 9:30 a.m. at the Sandra Day O'Connor U.S. Federal Courthouse in Phoenix.

(Reporting by Tim Gaynor and David Schwartz; Editing by Cynthia Johnston, Eric Walsh, Toni Reinhold)