In an emergency move to prevent the failure of a $450-million-asset Texas bank, the Federal Reserve Board yesterday permitted Mercantile Texas Corp., a major Dallas-based bank holding company, to buy Abilene National Bank, whose loan portfolio was riddled with bad energy credits.

Abilene National was the victim of a major run by its depositors several weeks ago after a story by the Dallas Morning News said the bank was near collapse.

But sources at the Federal Deposit Insurance Corp., which gave financial assistance to Mercantile to facilitate the purchase, said the bank would have failed whether or not there had been a run on deposits.

"It had big loan losses," an FDIC official said.

Abilene is the second major bank to feel the impact of declining oil prices on its oil-drilling customers. On July 5, Penn Square National Bank of Oklahoma City was closed by the comptroller of the currency because of huge loan losses.

Because federal regulators could not find another bank to take over Penn Square, credit unions and other depositors with $250 million of uninsured funds in the bank stand to lose as much as $50 million of those deposits.

The Penn Square failure became one of the most controversial in U.S. history for several reasons: huge depositing losses; the bank sold $2 billion of loans it made to other major banks, which reported huge losses on those loans; and the bank itself was heavily involved in promoting tax-shelter deals that went bad.

The FDIC said it made a $50 million, five-year deposit with Mercantile Texas Corp. to assist the big bank holding company with the Abilene takeover. The deposit will be interest-free for the first two years, at a cost to the FDIC estimated at $11 million. Mercantile Texas, which operates 23 banks in the state, will inject $20 million in capital into Abilene National and will put in more if it becomes necessary, the FDIC said.

In the complicated world of bank regulation, the comptroller of the currency was responsible for regulating Abilene National, but had to ask the Federal Reserve Board to approve the acquisition. The Fed regulates holding companies that own banks.

The FDIC, which insures the deposits up to $100,000, is responsible for either aiding the merger or, if a bank is closed, paying off depositors and selling the bank's assets to pay its creditors.