The government will run out of money if Congress fails to raise the debt ceiling, but no one can say when.

Because the government has borrowed up to the maximum allowed under law -- $1.824 trillion -- it cannot borrow any more to cover expenses unless Congress raises the limit.

Deputy Treasury Secretary Richard G. Darman said yesterday that he expects the government's cash balance to be negative, possibly today, and certainly by Wednesday. When the department's Financial Management Service determines that the balance is negative, it will notify the Federal Reserve. The Fed will then notify the nation's banking system not to honor government checks or electronic fund transfers, Darman said.

"In sum, unless a debt limit is passed promptly by the Congress . . . the United States would be in the position of defaulting on its obligations for the first time in history," he said.

No preference will be given to any checks, whether to Social Security recipients, defense contractors, people expecting to receive interest payments on government securities or others, Darman said.

In most cases, government checks to individuals for this month have already been distributed, officials said.

*Social Security checks were issued Thursday, and next month's checks are not scheduled to be delivered until the beginning of November.

*Federal retirement checks are mailed once a month, near the end of the month. October checks have been mailed, and next month's are not scheduled for delivery until Oct. 25 or 26.

*Federal agencies follow their own payroll cycles. However, an Office of Personnel Management official said yesterday that most pay employes on the second Tuesday of the pay period, today in the case of the current pay period. In many cases, however, checks are automatically posted to employes' accounts the previous day, or yesterday.

October fiscal crises have become the norm in recent years as Congress and the White House have butted heads over the budget. When the new fiscal year approaches on Oct. 1, Congress faces a deadline to pass appropriations bills. Last year, it also nearly ran out of time before the government bumped up against the debt ceiling, then $1.573 trillion.

This year, because Congress passed a continuing resolution to fund the government through mid-November, the government has the authority to continue functioning and paying employes. It does not, for the time being at least, have to shut down.

However, because Congress has not extended the debt ceiling yet, the government will not be able to borrow money. And without borrowing, it has nothing to spend.

The Reagan administration has sought an increase in the ceiling to $2.078 trillion, but the legislation has been held up by debate over a measure that would force the government to balance the budget by 1991.

The main result of the failure to raise the debt ceiling is that the government is unable to borrow by issuing bonds and shorter-term bills. The government had planned to auction bonds yesterday to get new cash and renew securities that have been issued, but officials said the government was unable to issue debt for cash yesterday.

Treasury officials said they were unsure when the government would be able to issue new debt again.

But financial analysts warned that when that day comes, the flood of new debt may clog the markets, increasing pressure on interest rates.

One option that Treasury has considered is turning to the Federal Financing Bank to issue securities to give the government cash, Darman indicated.

Congress established the FFB in 1973 to coordinate sales of government securities issued from independent federal agencies. It also has the authority to sell up to $15 billion worth of securities to the public, a Treasury official said.

What the Treasury could do is have the FFB issue securities to the government in return for cash to keep its cash balances from becoming negative, officials said. However, in letters to Congress earlier this month, Treasury Secretary James A. Baker III said that that practice was unprecedented and possibly could violate the intent of Congress in establishing the FFB.

In addition, debt issued by the FFB might have to pay a higher interest rate than regular Treasury securities, generally considered the least risky debt instruments around, officials said. Consequently, the FFB securities would be more costly to the government.

Another costly problem is that the government is obligated to invest several trust funds, such as the Social Security and railroad retirement funds, in Treasury securities so that they can earn interest. However, since Sept. 30, the government has been unable to do that because of the debt-ceiling problem. Darman said that failure to fully invest the trusts is costing the government about $8 million a day.