WASHINGTON (AP) — The Federal Reserve has auctioned $46.1 billion in safe Treasury securities to investment firms, part of an ongoing effort to ease credit stresses.

The auction — the ninth of its kind — was held Thursday and drew bids less than the $75 billion being made available.

In exchange for the 28-day loan of Treasury securities, bidding firms can put up as collateral more risky investments, including certain shunned mortgage-backed securities and bonds backed by federally guaranteed student loans.

The program began March 27.