UPDATE 2-U.S. Senate not ready yet for immigration debate

* Unclear if immigration reform to precede climate bill

* McCain says Arizona law caused by "enormous frustration"

* Mexico slams Arizona law (Adds Calderon comments, background, paragraphs 12-16)

By Thomas Ferraro

WASHINGTON, April 26 (Reuters) - The U.S. Senate is still a long way from debating any immigration reform despite renewed calls from President Barack Obama for an overhaul, a top Democratic aide said on Monday.

"We don't even have a bill yet," the aide said, adding that Democrats who control the chamber want to see such immigration legislation before deciding when to move to it, and that could take months.

Revamping U.S. immigration laws is one of Obama's top legislative priorities and the issue shot onto the agenda after Arizona passed tough legislation last week against illegal immigration.

Bipartisan talks on climate change collapsed on Saturday amid reports Senate Democratic Leader Harry Reid may move to push immigration legislation ahead of a planned climate change bill.

The senior Democratic aide said it remains uncertain whether immigration legislation will be brought up in the Senate before a climate change bill, or vice versa.

"Both are neck and neck in terms of importance to Democratic leaders in the House and Senate," the aide said.

The Obama administration is facing mounting pressure to overhaul immigration policy, as prominent Hispanic politicians and street protesters decry the new Arizona law as a violation of civil rights.

Republican Senator John McCain defended the new law in his home state of Arizona that requires police to question anyone who seems to be in the country illegally. It also forces immigrants to carry their alien registration documents at all times.

Speaking in the Senate, McCain attributed the measure to "the enormous frustration over the federal government's failure to carry out its responsibility to secure our borders."

Obama has denounced the law as misguided and has ordered monitoring of its implementation. White House press secretary Robert Gibbs warned that other states could also bring in tough immigration laws if there is no overall reform.

"Look at what's happened in Arizona," Gibbs said at the White House. "That's because the United States at the federal level has failed to act .... There's room for progress."

Mexican President Felipe Calderon slammed the Arizona law.

"Criminalizing immigration, which is a social and economic phenomena, this way opens the door to intolerance, hate, and discrimination," Calderon said.

ELECTION YEAR

The immigration issue poses dangers for both Republicans and Democrats in November congressional elections.

Republican efforts to regain lost ground with Hispanics, the country's biggest and fastest-growing minority, could face fatal blows if the party opposes immigration reform.

But an immigration overhaul could further inflame conservatives already enraged by Obama's spending and healthcare initiatives.

Republican Senator Lindsey Graham accused Reid on Saturday of playing election-year politics with immigration and withdrew his support from an anticipated accord on a climate bill.

Reid is in a tough campaign for reelection in November in his home state of Nevada, and pushing immigration reform could help energize Hispanics, a key voting group.

While Graham has been trying to reach an agreement on climate legislation, he's also been working for months with Democratic Senator Charles Schumer on a possible bipartisan immigration bill.

They aim to bolster border security, create a new process for admitting temporary workers and implement a "tough but fair path" to U.S. citizenship for illegal immigrants in the United States. Reid could declare talks stalled and offer a bill of his own.

A top business lobbyist said Reid had created confusion with the immigration push.

"Right now," the lobbyist said, "I have no idea ... what direction Reid plans to go."

Chris Krueger of Concept Capital, a private firm that tracks Congress for institutional investors, said: "I think the chances Congress passes immigration reform (this year) are slim to none -- and slim just left the building."

"Maybe they're teeing it up for next year," Krueger said. (Editing by Alistair Bell and Eric Walsh)