The federal government ran up a $48.1 billion deficit in November, a 62 percent increase over a year ago, due in part to the Persian Gulf buildup and a failing economy, the Treasury Department reported Friday.

Combined with the October deficit, the imbalance for the first two months of fiscal 1991 totaled $79.5 billion, up 42.5 percent from the comparable period of fiscal 1990.Economist Michael K. Evans, head of a Washington forecasting firm, said the weakening economy is resulting in declining tax revenues.

"It's really getting to the point where the deficit is starting to balloon because both personal and corporate taxes are starting to fall off," he said. "Receipts in November were $6 billion less than they should have been in a normal economy."

The government collected $27.2 billion in individual income taxes last month, a 21 percent decline from November 1989. At the same time, corporate income taxes were down 46 percent to $1.3 billion.

At the same time, defense spending increased 18 percent from a year ago, to $29 billion, reflecting the military buildup in the Middle East. And spending on the savings and loan bailout jumped to $2.8 billion, up 220 percent from the $879 million outlay in November 1989.

Overall, receipts totaled $72.8 billion in November, up 2.3 percent from the same month last year. Spending, however, jumped 20 percent, from $100.9 billion in 1989 to $120.9 billion last month. The deficit is the difference between the two.

The Bush administration already has conceded the fiscal 1991 deficit will break a record. Budget director Richard Darman has projected the imbalance at between $250 billion and $300 billion.

The Congressional Budget Office, on the other hand, forecasts a $320 billion gap this year.