SAN JUAN, Nov 20 (Reuters) - Puerto Rico's Government Development Bank on Friday presented some of the island's creditors with more details on a forthcoming plan to consolidate their bonds into a single bond exchange, in a meeting the GDB's president called "very positive and productive."

Melba Acosta, the president, spoke to reporters after a meeting between the GDB and advisers to some of the U.S. territory's financial creditors in New York.

GDB has said it plans to offer creditors a universal debt exchange, or "superbond," which in essence would allow bondholders across several Puerto Rican credits to exchange their debt for a single new bond.

But with existing bonds backed by different revenue streams from the various issuing authorities, such as the GDB itself and Puerto Rican sales tax authority COFINA, Acosta said revenue streams might be consolidated to support the new bond.

"If we have different credits that have different repayment sources ... there will most probably be a consolidation of repayment sources," Acosta said.

The bond offer may also include variations to accommodate the details of different bond agreements, rather than a strict one-size-fits-all approach, said Acosta, who did not attend the meeting but was briefed on it.

Puerto Rico is in the midst of an economic crisis, facing a 45 percent poverty rate, heavy emigration to the mainland United States and $72 billion in debt.

Its governor, Alejandro Garcia Padilla, has called for concessions from bondholders but has faced resistance, with creditors demanding his administration do more to reform spending.

Friday's meeting in New York was open to creditor advisers who had signed nondisclosure agreements, only about 15 percent, according to a Friday note by Height Securities Puerto Rico analyst Daniel Hanson.

Acosta said attendees included lawyers and financial advisers to holders of general obligation bonds, which carry constitutional protections; bonds issued by the GDB; COFINA bonds; and cooperatives and mutual funds with exposure to Puerto Rican debt.

The meeting comes ahead of a Dec. 1 hearing about Puerto Rico before the U.S. Senate Judiciary Committee, as Congressional Republicans mull whether to support legislation that could help Puerto Rico restructure its debt.

Dec. 1 is also the day when Puerto Rico owes $355 million in bond payments on which some analysts have said it is likely to default.

Hanson said Friday's creditor meeting might have been an attempt to "demonstrate to the U.S. Congress that the GDB is serious" about government reforms.

(Reporting by a contributor in San Juan; Editing by Leslie Adler)