WASHINGTON (AP) — Federal regulators are set to require big banks to keep enough high-quality assets on hand to survive during a severe downturn, the latest move under congressional mandate to lessen the likelihood of another financial meltdown.

The Federal Reserve and two other agencies moved toward adopting rules Wednesday that will subject big U.S. banks for the first time to so-called "liquidity" requirements. Liquidity assures the ability for banks to access cash quickly.

The largest banks — those with more than $250 billion in assets — will have to hold enough cash, government bonds and other high-quality assets to fund operations for 30 days during a time of market stress.

Regulators also are giving banks leeway in requiring collateral from companies that use derivatives to guard against price swings.