ONE MORNING IN October 1992, Arkansas Gov. Bill Clinton ate breakfast with Hugh McColl Jr., the chairman and CEO of Charlotte, N.C.-based NationsBank. Clinton's presidential campaign was winding down, and the Southern banker thought it was a good time to get to know the Southern governor who'd soon be president.

Though no one knew it at the time, that meeting may prove to be one of the most important in the history of American banking.Only McColl and Clinton know exactly what was discussed at the breakfast. But soon after the meeting, McColl gave a ringing, 11th-hour endorsement of Clinton, after having supported Clinton's two opponents, Ross Perot and George Bush.

Once elected, Clinton returned the favor by championing McColl's favorite cause: interstate banking. It was Clinton's decision to sign a 1994 bill removing those barriers that paved the way for last week's historic merger between Nations-Bank and BankAmerica.

McColl and Clinton became fast friends. The banker became a frequent guest at the White House, where he and Clinton once stayed up late into the night discussing banking issues.

McColl himself has come a long way since 1983, when he took over the small North Carolina National Bank, which later became Nations-Bank. Throughout the 1980s and early 1990s, he aggressively acquired smaller banks.

His buying spree set the stage for last week's deal, which made BankAmerica the largest player in a rapidly consolidating industry. All that was needed was for interstate banking to become law - which officially took effect last June.

McColl has become the George Washington of American banking, presiding over a revolution in the industry that has made him the most powerful banker in the country - by far.

"I think (McColl) will loom, frankly, as a historic figure," Ken Guenther, executive vice president of the Independent Bankers Association of America, said. Guenther and other industry sources believe McColl's fingerprints are all over the interstate banking bill.

A NationsBank spokesman denied that any undue influence was exerted. "It's part of the responsibility of the banking industry to consult and give information to the legislature - and that would include the president - when laws are being written," NationsBank's Lynn Drury told us. "So the fact that (Clinton) might ask (McColl) what he thought about something, or ask for (McColl's) input on something, would be part of the process."

Yet Guenther thinks McColl's relationship with the president has gone beyond routine consulting. The frequent socializing of the two men seems to bear him out.

McColl acted every bit the conquering hero at the New York news conference announcing the merger. "I wouldn't say win at all costs, but I like winning," McColl gloated.

There will be no power struggle for control of the new BankAmerica. Said BankAmerica chairman and CEO David Coulter, who will now be McColl's No. 2: "It was very obvious, I think, to all of us that Hugh McColl was the right person to be CEO."

Hugh McColl doesn't take a back seat to anyone. And it wouldn't have happened without a friend in the White House.