NEW YORK, July 16 (Reuters) - Investors requested $668.9 million in loans for legacy commercial mortgage-backed securities on Thursday in a slow start for a key government program aimed at reviving the commercial real estate market.

The Fed is offering loans to investors for commercial mortgage-backed securities under its Term Asset-Backed Securities Loan Facility, or TALF, in an attempt to revive markets both for new and existing commercial bonds.

Lowering lending costs in commercial real estate could help ease refinancings by borrowers, who are increasingly defaulting on loans for a lack of credit.

Thursday was the first time the Fed accepted existing bonds under the TALF and the second round for its newly issued CMBS TALF program.

Investors did not request loans for newly issued CMBS in June or July. (Reporting by Kristina Cooke; Editing by Dan Grebler)