UPDATE 2-Row on Mexican left seen delaying oil bill

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By Catherine Bremer

MEXICO CITY, March 24 (Reuters) - A leadership spat in Mexico's left-wing opposition party could delay a government attempt to make politically difficult changes to oil sector laws, a top ruling party senator said on Monday.

Conservative President Felipe Calderon had been awaiting the result of the left's March 16 leadership contest before presenting an energy bill, lawmakers say, but a row over the vote count means he is unlikely to submit the bill this week as many expected.

"It's not very likely. It's not impossible but it's unlikely," Sen. Gustavo Madero, a member of the Senate energy committee, told Reuters.

Calderon is keen to have the left-wing Party of the Democratic Revolution, or PRD, Mexico's second political force, take part in a congressional debate on oil reform, but is loath to present a draft bill until he knows whether a moderate leftist or more radical rival will be heading the party.

After a weekend of bickering by PRD officials, the ruling party's lower house coordinator Hector Larios said the government's energy proposal should be ready in 10 to 15 days.

The Senate energy committee has been debating for weeks about how energy laws could be changed to help state energy monopoly Pemex shore up flagging oil output and reserves.

Calderon had hoped to pass energy legislation before the current congressional session ends on April 30.