UPDATE 1-GM, Peugeot mull joint venture -report

(Adds Peugeot no comment, shares, detail, background)

PARIS, Oct 12 (Reuters) - General Motors and PSA Peugeot Citroen are working on plans for a joint venture as they flesh out the carmaking alliance announced earlier this year, La Tribune reported on Friday.

Detroit-based GM would place Opel in the 50-50 venture along with its French partner's core manufacturing division, according to the newspaper, which cited anonymous sources.

GM and Peugeot both declined to comment on the report, which also said the U.S. automaker could inject more cash into the joint venture. " We haven't commented on previous reports and we're not going to on this one," Peugeot spokeman Jonathan Goodman said.

Peugeot "remains focused" on operational working groups due to report back by the end of the month on several potential joint vehicle programmes, Goodman said.

Peugeot shares rose on the report and were 4 percent higher at 1443 GMT, while GM stock was down 0.2 percent.

The U.S. automaker paid 320 million euros for a 7 percent stake in Peugeot in March as part of the original alliance deal, though the French automaker's shares have since plunged.

But the proposal is likely to run into objections from the French government and has yet to be submitted to the Peugeot board, the report added.

GM and Peugeot announced their alliance plans in late February with the goal of saving at least $2 billion annually within five years, evenly split between the partners.

Paris-based Peugeot outlined five possible joint vehicle programmes following talks with unions in March: a family of small cars for emerging markets; larger sedans; a fuel-efficient subcompact design; compact crossovers or SUVs; and a dual-clutch transmission.

(Reporting by Laurence Frost and Ben Klayman; Editing by James Regan and Christian Plumb)

((laurence.frost@thomsonreuters.com)(+33 1 49 49 56 83)(Reuters Messaging: laurence.frost.thomsonreuters.com@reuters.net))