Inflation at the wholesale level jumped a surprising 0.9 percent in October, reflecting the higher cost of automobiles and perhaps the first signs that the falling dollar is affecting prices.

The increase in the producer price index last month was the sharpest one-month rise since April 1981, when prices at the wholesale level rose 1 percent, the Labor Department said yesterday. The October rate of increase, if continued for a full year, would be 10.8 percent.

Although economists said that many of the factors contributing to the steep price rise last month would not recur, they said the long decline in wholesale prices probably has ended. In the last 12 months, the producer price index has risen only 1.1 percent. These price increases eventually work their way into the retail level and show up in the consumer price index, which rose 3.2 percent in the last 12 months.

Economists said that prices are beginning to feel the effects of the decline of the dollar since February. A cheaper dollar makes foreign goods sold here more expensive and also allows competing domestic suppliers to raise their prices. The effects are usually felt first in commodities, economists said.

After months of decline, prices of some commodities have begun to firm as a lower dollar has given more purchasing power to the currencies of other countries and increased the demand -- and therefore the price -- for these products, economists said. Raw materials prices increased 3.1 percent last month following 10 months of declines.

Other economists attributed the sharp jump in raw materials prices in part to an increase in the cost of cattle and hogs after livestock producers had cut back herds.

Automobile prices were sharply higher with the introduction of new models and the end of discount financing programs on the remnants of the 1985 fleet.

"The dollar decline is creeping into the producer price index," said Allen Sinai, chief economist for Shearson Lehman Bros., who said other indexes of commodity prices already have started climbing.

Wholesale inflation will double next year from this year's rate, to 2.5 percent, said David Wyss, economist with Data Resources Inc. "There will be a slight acceleration because of the dollar going down. We'll start seeing it gradually." However, compared with past years, inflation will "still have a modest performance."

Some economists doubted that prices would feel the pressure of the dollar decline this soon.

Paul Getman, economist for Chase Econometrics, said that price changes "are fairly quick" to show up for some commodities, but suppliers are often bound by contracts negotiated months ago.

But even if the increase in wholesale-level prices last month were not caused by the dollar, its fall will soon be felt.

In addition to increasing the relative price of imports, a lower dollar means that foreigners are able to use their currencies to buy more goods that are sold for dollars, improving their purchasing power, economists said. Because foreigners can purchase more, their demand for products will rise, reducing the supply of those goods and raising their prices.

Sinai said, for example, that prices of crude materials, excluding food and energy, increased 0.5 percent last month.

However, other economists said that the abundance of commodities on world markets and continued weakness in oil prices will tend to moderate price increases.

Passenger car prices were 4.9 percent higher in October than in the same month in 1984, the Labor Department said. Beef and veal prices rose 11.8 percent and pork prices rose 9.9 percent in October after declining in September. Prices also rose for processed poultry, soft drinks, eggs and milled rice. Prices fell for fresh fruits and vegetables, dairy products and fish.

Prices also declined for gasoline and natural gas, while increasing for home heating oil.

In a separate report, the Federal Reserve Board said that production at the nation's factories, mines and utilities was unchanged in October after dropping 0.1 percent in the previous month.

Manufacturing production was unchanged after declining 0.2 percent in September, largely because of a 6 percent decline in output on automobile assembly lines. Production dropped in large measure because of a brief strike at Chrysler Corp.

Production at the nation's mines dropped 1.4 percent, the fourth consecutive monthly decline, and output at utilities fell 0.2 percent, following a 1.8 percent increase in September.