Next week, stockholders of MNC Financial Corp. will open their mailboxes to find $24 million in dividend checks representing their share of the big banking company's profits.

MNC, however, isn't making a profit.

The holding company that owns Maryland National, Equitable and American Security banks lost $75 million in the latest three-month period and is widely expected to run in the red for the year as the result of real estate loans gone bad.

But despite the mounting losses, MNC has continued to pay dividends to shareholders, a decision that troubles federal banking regulators and many members of Congress who are involved with banking issues.

MNC is by no means the only unprofitable banking company that is continuing to pay dividends. Yesterday, Perpetual Financial Corp., which has lost $69 million in the last nine months and has warned stockholders to expect future financial problems, declared $1 million in quarterly dividends on its preferred stock.

The only way a bank that is losing money can pay dividends is by dipping into its capital -- the cash that represents the stockholders' stake in the bank. When a financial institution is facing difficulties, it should be building up its capital rather than giving it back to shareholders, the regulators say.

By continuing to pay dividends when they get in trouble, banks and savings and loans often make failures more costly to the taxpayers, say Sen. Donald W. Riegle Jr. (D-Mich.) and Rep. Henry B. Gonzalez (D-Tex.), chairmen of the Senate and House banking committees.

They cite the case of National Bank of Washington, which paid its shareholders $500,000 in dividends last April and failed barely four months later, leaving hundreds of millions of dollars in losses to be covered by the Federal Deposit Insurance Corp. If that final dividend hadn't been paid, NBW would have cost the FDIC half a million dollars less than it is going to.

A flat ban on payment of dividends by banks and savings and loans that are losing money or are in other financial trouble is advocated by Gonzalez and Riegle in packages of banking reform legislation being prepared by the two influential lawmakers.

Bankers argue that cutting the dividend is not necessarily the best way for them to raise capital and may even hurt. When a dividend is skipped, the price of the stock drops, making it harder to raise capital by selling more shares, they say.

After reporting that it expects a $625 million third-quarter loss and has decided to lay off 5,000 employees, Chase Manhattan Corp. said Friday it would still pay stockholders a quarterly dividend of 30 cents a share -- less than it had paid, but still almost half what shareholders were getting when the bank was profitable. The holding companies that own Bank of New York, Chemical Bank, Citibank and First Chicago Bank are all continuing to pay dividends even though they do not meet new federal capital requirements that will soon go into effect.

Chase's dividend payments were criticized by several lawmakers at a House Banking Committee hearing Tuesday. Ailing financial institutions that continue to pass out cash to shareholders may turn out to be "paying their dividends with taxpayers' money," Rep. Jim Leach (R-Iowa) said at a congressional hearing this week.

"One problem is that we have allowed those institutions to pay dividends and to deplete their capital," said Leach, criticizing federal regulators for permitting the payouts.

"I do not think undercapitalized institutions ought to be paying dividends," agreed FDIC Chairman L. William Seidman. "I do not think that represents the best interest of the banking system."

All four of the federal agencies that regulate banks and savings and loans have regulations limiting dividend payments by struggling institutions. "Our policy is they shouldn't pay dividends unless they can afford it. Dividends ought to come out of earnings, not out of capital," said a Federal Reserve spokesman, summing up the rules of all the regulators.

Those rules are not enforced effectively, so the restrictions need to be written into law, the congressional critics say.

Officials of both Perpetual and MNC said their dividend payments are being made with the full knowledge and advance approval of federal regulators.

Because of its widely reportedly financial problems, MNC's stock has fallen so low that the dividend payments amount to an annual yield of almost 18 percent, the highest of any major bank, the trade newspaper American Banker reported this week.

Even investment analysts who usually act as advocates for shareholders are skeptical of whether such high dividends ought to be paid. "I was surprised that they declared the full dividend for the quarter," said Kyle Legg, a specialist in banking stocks for Alex. Brown & Co. in Baltimore.

Rather than paying out cash to shareholders, banks ought to be building up their capital, she said. "Capital is the name of the game. The banks that are going to have the best chance of success in the '90s are those with the strongest capital."

MNC meets both the current capital standards for banks and tougher standards that go into effect in January 1992, a spokesman said. Perpetual, however, meets only the current requirements and has disclosed that it may not be able to clear the higher capital barriers that are coming.

Despite that impending problem and the continuing losses, Perpetual's board of directors voted to pay the usual dividend because "we have $31 million in cash that should give the shareholders a comfort level," said spokesman Robert A. Barton Jr.

Acknowledging that the decision "might conflict with what Mr. Riegle and Mr. Gonzalez want," he said Perpetual's "loss has mainly been provided for; hopefully if the {real estate} market conditions turn around ... we can get this thing profitable again."