Several major New York banks, led by Chase Manhatten, raised their prime lending rates to 18 percent yesterday, the highest level for almost two months.

Chase, the nation's third-largest bank, moved in response to sharp rises in the cost of funds in the past two weeks as the Federal Reserve has attempted to rein in the money supply.

Many forecasters expect this to ease in coming weeks, and therefore do not predict sharp or continued rises in interest rates. But yesterday's increase goes against the administration's prediction that interest rates will fall sharply by the end of the year. The Treasury also announced yesterday a one-point rise in the interest rate on U.S. savings bonds to 9 percent.

Meanwhile, the Commerce Department yesterday reported a 1.4 percent rise in March in the leading economic indicators. These are supposed to foreshadow changes in the economy. This was the first rise in the index since November, despite evidence from other economic data that the economy continued to grow strongly in the first three months of this year.

But much of the increase came because of higher oil prices, early in the year. One of the measures used in the composite index of leading indicators reflects changes in the prices of sensitive raw materials, because these often move in response to changes in demand.

Other indicators which contributed to the increase were a rise in the average work week, slower deliveries, contracts and orders for plant and equipment after allowing for inflation, stock prices, and the money supply in constant-dollar terms.

But the March rise was not an indication that the economy is going to grow strongly, economist Sandra Shaber of Chase Econometrics said yesterday. "For all of the strength in the first quarter, much of it was dissipated by March," she said.

The Commerce Department said that if the effect of higher oil prices were taken out of the index, a rise of just 0.2 percent would have been recorded for March. The overall index stood at 137.1 last month compared with a 1967 level of 100.

"It's hard to say that an increase in oil prices reflects a real improvement in the economy, especially when the oil price hike was the result of deregulation, and not demand," a Commerce analyst said.

There has been a string of surprisingly food figures on the economy in recent weeks. The administration nevertheless claims that its program of tax and spending cuts is needed to improve an ailing economy. President Reagan contended last night that enactment of his proposals is the only way to cure the extend of the economy's sickness.

The tighter money markets have partly been due to technical factors. One of these is that M1-B figures recently have shown strong growth, but have not been fully adjusted for seasonal variations. The Fed has been pursuing a tight-money policy which may be eased if the bulge in M1-B is passed.

Beryl Sprinkel, Treasury undersecretary for monetary affairs, told reporters yesterday that interest rates would fall if the president's program were followed, but he did not know when.

He announced that the quarterly financing requirements of the Treasury are $6.75 billion of securities to be sold in May.

During the third quarter, the Treasury expects to borrow between $16 billion and $19 billion net, assuming a $15 billion cash balance at the end of September.

The details of next week's offering are as follows:

$3 billion of 3-year notes, minimum denomination $5,000, deadline for receipt of tenders 1:30 p.m. next Tuesday.

$1.75 billion of 10-year notes, minimum denomination $1,000, deadline for receipt of tenders 1:30 p.m. next Wednesday.

$2 billion of 30-year bonds, minimum denomination $1,000, deadline for receipt of bids 1:30 p.m. next Thursday.

Bids may be sent to any Federal Reserve bank or to the main Treasury building in Washington.