Led once again by food and fuel, producer prices for finished goods rose 1.4 percent in September, the largest monthly increase in nearly five years, the Labor Department reported yesterday.

Soon after the figures were released, James McIntyre, director of the Office of Management and Budget, said the administration's estimate of a 10.6 percent rise in consumer prices for 1979 appears to be on the low side and will soon be revised upward.

At the White House, press secretary Jody Powell said President Carter remains hopeful that inflation will slow this year. He stopped short, however, of repeating previous claims by administration officials that inflation would fall below double-digit rates before the end of the year.

Finished goods are eventually sold to retailers, and the 15.7-percent rate of inflation in their prices over the last three months is already hitting retail stores.

The producer price index (formerly the wholesale price index) for consumer foods rose 1.8 percent in September, matching the high rates of January and February, compared with 1.2 percent in August. Beef and veal prices rose sharply after four months of decline. Pork, poultry, coffee and bakery goods also rose.

The energy portion of the finished goods index climbed 6.8 percent in September, more than the 6.2 percent and 5.8 percent increases in July and August. Home heating oil rose the fastest, 7.9 percent.

Since September 1978, gasoline prices charged by refiners have risen 52.5 percent, and heating oil prices 72.8 percent, the department reported.

Other major increases over the last year include rice, up 38.4 percent; beef and veal, 22.6 percent; fish, 18.3 percent; footwear, 21.6 percent, and automobile tires and tubes, 19 percent.

The administration's hope is that the string of big monthly increases in energy prices will end soon as the full effects of the increase in world crude oil prices are passed through to consumers. But the renewed increase in food prices, if it continues, could keep the overall inflation rate soaring.

The brightest spot in the finished goods index last month was capital equipment, mostly goods bought by business, whose prices rose 0.3 percent. Such prices went up 0.1 percent in August, but had aveaged an 0.8 percent increase during the first seven months of this year.

The index for intermediate materials, which still requires further processing, rose 1.5 percent in September. The index for crude materials rose even more, 2.1 percent, primarily because of 9.4 percent increase in crude oil prices.

Grain prices fell 2.1 percent in September, but were still up 26.9 percent from a year ago. The announcement this week by the administration that the Soviet Union is free to buy up to 25 million metric tons of wheat and corn during the next 12 months could cause grain prices to rise again, analysts said.

Among intermediate goods, flour prices dropped by 1.5 percent last month, but remained 27.1 percent higher than last year. The surge in flour prices followed a big jump in wheat prices, and it has already helped push up the cost of bakery goods sold to consumers.

While most of the focus has been on oil prices, the cost of natural gas is also up. Crude oil prices rose 38.1 percent in the last 12 months, but natural gas prices rose nearly as much, 35.7 percent.

Labor Department economist Craig Howell said analysts could not be sure when the crude oil price increases would finish filtering through the U.S. economy.

"It takes a while for those things to work their way through the system," Howell said. "It's hard to say when the last round of OPEC price [increases] will work its way through."

Meanwhile, reports persists that some Organizationof Petroleum Exporting Countries members intend to raise their prices soon. Nigeria plans some increases and other countries, including Libya, are selling increasing amounts of crude oil on spot markets for prices $10 to $15 a barrel above their official selling prices.