UPDATE 1-Obama warns of 'misguided' immigration efforts

* Obama refers to America's "broken immigration system"

* Democrats may push immigration reform effort in Congress

* Arizona governor enacts tough immigration law (Updates with Arizona measure signed into law)

By Tabassum Zakaria

WASHINGTON, April 23 (Reuters) - President Barack Obama on Friday warned that without federal immigration reform the door would be open to "misguided efforts" such as a new Arizona law that has raised questions of civil rights.

Obama pressed for immigration reform at a White House Rose Garden ceremony in which 24 members of the U.S. military originally from China, Mexico, Ethiopia and other countries became American citizens.

"Today we celebrate the very essence of the country that we all love -- an America where so many of our forbearers came from someplace else," said Obama, whose father was Kenyan.

"And so on a day like this, we are also reminded of how we must remain both a nation of immigrants and a nation of laws," he said. "This includes fixing America's broken immigration system."

Just hours after Obama singled out the Arizona measure as threatening "to undermine basic notions of fairness that we cherish as Americans," the state's Republican Governor Jan Brewer signed into effect the toughest immigration law in the United States.

Police in the border state with Mexico will now be required to determine if people are in the country illegally if there is "reasonable suspicion," which critics charge will open the door to racial profiling.

Democratic leaders in Congress are weighing whether to try this year to push through immigration reform, a contentious issue in the United States where about 10.8 million illegal immigrants live and work in the shadows.

Obama's Democratic Party fears a political backlash from Hispanics in the November congressional elections because the issue has made little headway since Obama took office. But many conservatives oppose easing the pathway to citizenship for illegal immigrants and complain they drain resources and take jobs from U.S. citizens.

"Our failure to act responsibly at the federal level will only open the door to irresponsibility by others," Obama said.

The Arizona law requires state and local police to arrest people who are unable to provide documents proving they are in the country legally. It is expected to spark a legal challenge.

"If we continue to fail to act at a federal level, we will continue to see misguided efforts opening up around the country," Obama said.

Before Arizona's governor signed the measure, White House spokesman Robert Gibbs said Obama had asked that the Justice Department look into any civil rights implications if it became law.

Hispanics were key to Obama winning Nevada in the 2008 presidential election and may determine if Senate Democratic leader Harry Reid wins another six-year term representing that state in November.

Congressional leaders have discussed taking up immigration reform this year, but after the hard-fought healthcare reform battle it may be difficult to get another highly controversial bill through Congress before the elections.

(Additional reporting by David Schwartz, editing by Vicki Allen)