UPDATE 1-Mexican left ends Congress sit-in over oil plan

(Updates with quotes, details)

By Miguel Angel Gutierrez

MEXICO CITY, April 25 (Reuters) - Left-wing Mexican lawmakers protesting an oil reform proposal they see as creeping privatization ended a two-week congressional sit-in on Friday after ruling conservatives and their centrist allies offered a broad debate on the issue.

Dozens of left-wing deputies and senators had disrupted the upper and lower houses with round-the-clock protests since April 10 to block conservative President Felipe Calderon's plan to shake up the oil sector and increase private-sector involvement.

The Party of the Democratic Revolution and some smaller allies see the measure as a sneaking privatization of Mexico's oil industry, expropriated in 1938, as Calderon attempts his most ambitious economic reform to date.

The blockade by the second largest voting group in Congress forced lawmakers from the ruling National Action Party, or PAN, and the centrist opposition to convene outside the main chambers for the first time in nearly two decades.

"Today we are concluding a successful stage in the movement. We prevented a fast-track approval of the proposals," said Carlos Navarrete, the left's coordinator in the Senate, as lawmakers sang the national anthem to mark the end of the protests.

Leftists folded up a huge banner that covered the lower house's entire rostrum, took chains off doors and returned many seats after using them as beds and barricades to stop rival lawmakers from getting on to the floor of the chamber.

Calderon wants to sweeten oil field service contracts with bonus fees to attract experienced foreign partners that could help state monopoly Pemex uncover new deepwater oil deposits and shore up declining output and reserves.

Calderon had hoped to get the proposal approved before Congress wraps up its spring session next Wednesday. Instead, lawmakers will hold an open debate on the oil industry, bringing in independent experts, from May 13 to late July.

"Many have given their word that once the debate is over, the commissions will meet to discuss (the energy reform) and pass judgment," said Senate President Santiago Creel, a member of PAN.

"That is the commitment and I am sure that all of us who signed this agreement will honor it," he added.

Mexico is the world's sixth largest producer of crude oil, according to the U.S. Energy Information Administration, and the No. 3 supplier of oil to the United States.