UPDATE 2-Cemex gains on debt news, but questions remain

* Cement maker's shares rise as debt deal looks imminent

* Cemex says all creditors support restructuring plan

* Key details of plan still unknown (Recasts; adds detail on restructuring, analyst comment)

By Robert Campbell

MEXICO CITY, Aug 11 (Reuters) - Shares in Mexican cement maker Cemex rose on Tuesday after the company said its lenders backed a vital debt restructuring, but details of the plan, which could include an issue of new shares, remain unclear.

The world's No. 3 cement producer said after the markets closed on Monday that it had the backing of all of its creditors for a plan to extend the maturities of $14.8 billion in debt due in 2009 through 2011.

The restructuring is likely to carry a large fee and Cemex will likely have to issue new shares under the plan, Deutsche Bank analyst Dan McGoey said in a research note.

"Cemex had outlined as a key risk that an equity issuance would likely be a component of its current refinancing initiative ... The most crucial variable is the magnitude of equity issuance creditors require in exchange for full support," McGoey wrote.

A Cemex spokesman declined to comment beyond noting that the company had previously said an equity issuance was a possibility.

Cemex shares in Mexico City (CMXCPO.MX) rose 1.71 percent to 14.30 pesos after earlier trading up nearly 6 percent. The company's U.S. shares (CX.N) rose 0.73 percent to $10.99.

Amid a steep global downturn in construction, Cemex has been under immense pressure to reach a deal to extend debt it took on to finance its acquisition of Australia's Rinker in 2007. (Additional reporting by Michael O'Boyle and Gabriela Lopez, editing by Gerald E. McCormick)