Two major U.S. banks raised the key prime lending rate from 15 3/4 percent to 16 1/2 percent yesterday, as other short-term rates climbed and credit tightened. Some experts fear that higher interest rates could stall an economic recovery that has been forecast this year.

Interest costs to the government, as measured by the weekly Treasury bill auctions, also rose yesterday to the highest levels since Oct. 5. The average yield on three-month Treasury bills climbed to 13.85 percent from 13.364 percent a week earlier, while six-month bills climbed from 13.53 percent to 13.846 percent.

More increases in the prime rate--charged by banks to top business borrowers--are expected this week in the wake of yesterday's sharp boost by Citibank of New York and Crocker National of San Francisco, analysts said. Some market participants also believe the Federal Reserve, the nation's central bank, may raise its discount rate, charged to member banks for borrowing, from the 12 percent level set in early December.

Several major banks--including Chemical, Marine Midland and Irving Trust, all in New York--raised their broker loan rates to 16 percent yesterday. Changes in these rates, charged to stock brokers for short-term loans, often foreshadow changes in the prime.

The prime rate fell to 15 3/4 percent just two months ago. A few banks moved their rates down to 15 1/2 percent in early December but soon came back up to the industrywide level. At the time, many analysts expected the prime to go down.

Since then, however, other short-term interest rates have risen sharply, pushing up the cost of funds to the banks. The federal funds rate, charged on overnight funds that the banks lend to each other, rose as high as 16 percent during the day yesterday compared with a 13.98 percent average in the week ending last Wednesday.

Yesterday's rates rise was linked to the recent surge in money growth. Market participants fear that the Fed will tighten credit and push up interest rates in response to the sharp and apparently unintended increase in the money supply since November.

Last Friday the Fed announced a much smaller drop in the money supply than had been expected, which increased alarm about a likely tightening up by the Fed. However, William Sullivan of Bank of New York said yesterday that some banks may "want to drag their heels" in raising their prime rates "to see if the money supply bulge washes out later this month." With business loan demand down because of the recession, banks have to compete more heavily for funds, so they may be reluctant to increase their interest rates too soon.

The general rise in rates comes much earlier in the business cycle than usual, and will make the economic recovery very sluggish if it continues, many analysts have said. And a combination of tight money and large projected federal budget deficits will ensure relatively high interest rates for some time to come, according to leading economists.

As a result of earlier falls in Treasury-bill yields, the interest rate on small-saver certificates will decline today to 14.55 percent from 14.75 percent for savings institutions, and to 14.3 percent from 14.5 percent for banks, Treasury said.

At the T-bill auction yesterday, $5 billion each of three-month and six-month bills were sold. The investment rate, or equivalent coupon-issue yield on three-month Treasury bills at yesterday's auction was 14.55 percent, and on six-month bills 15.1 percent. Based on the auction, the ceiling rate on six-month money market certificates at banks and savings associations will rise to 14.096 percent today from 13.78 percent.