It's a scene right out of "The Mouse That Roared": The president of the tiny National Consumer Cooperative Bank, faced with an impoundment of its funds by the president of the United States, writes her agency a check for $60 million -- and the Treasury Department surrenders the money without a fight.

The heist pulled off successfully, a couple of days later she hand-delivers a letter to Treasury Secretary Donald Regan thanking him for "expeditiously responding" to an earlier request for funds.

Now Treasury Department officials are miffed, since they had no intention of handing over the funds in the first place. So they held a press conference yesterday, demanding that NCCB President Carol Greewald return the money.

It she doesn't, the department says, they will take the matter to the Department of Justice. She says she's going to keep the money unless Congress tells her not to.

"This is a disgraceful example of power politics," Greenwald said yesterday about the Treasury threat.

Asked how Greenwald could have pulled off her mini-coup, David R. Brennan, acting general counsel at Treasury, said there are 14,000 "certified officers" -- including Greenwald -- who can present vouchers to a Treasury disbursement office and get funds. With that many officers and vouchers, the Treasury can't cross-check all of them to see if they are really entitled to the money.

The system has been in effect for 25 years, and there hasn't been any problem with it before now, he said.

Greenwald says the administration wouldn't dare go to the Justice Department, because it knows the bank has legality on its side.

The Office of Management and Budget, using the Treasury Department as a "front," actually is just making the bank a hot political issue so Senate Republicans will fall in line behind the president, says Greenwald.

President Reagan not only wants to rescind the bank's funds, he wants to eliminate the entire bank by September. The House Appropriations Committee recently approved funding for the NCCB, however, and the Senate Banking Committee yesterday approved a plan by which the bank would be kept alive though with great limits on what it can do.

These victories for the bank are what prompted the Treasury's threats yesterday, Greenwald charged.

On the cooperative bank's side is a General Accounting Office report, issued on April 13, which said the administration cannot impound the bank's funds pending congressional action on the presidential request to take the money away.

The Treasury's Brennan admits the department action is at variance with the GAO finding. He explained, however, the Treasury believes, while the GAO opinion is "entitled to deference," it is not binding.

The NCCB and House Banking Chairman Fernand St. Germain (D-R.I.) say the GAO ruling is binding.

When she sent the voucher over for the funds, she says she didn't know what would happen.But now that the bank has the funds, it's not giving them up, Greenwald adds.

If Congress votes a rescission or an end to the bank's charter, she will return it. The rescission request must be acted on within 45 days, which is May 11.

The bank isn't spending the money yet, but will starting on May 12 unless Congress acts, she said.

Before the fracas broke into the open with the Treasury's press conference yesterday, the bank and Treasury were negotiating a kind of intragovernmental out-of-court settlement, Greenwald said.

And that is what she plans to continue to do next. Her guerrilla tactics around the administration structure accomplished, Greewald now wants quiet diplomacy. Asked what her next move is, she says: "We'll talk about it like civilized adults ina civilized society."