Small increases in energy and food costs led to a moderate 0.3 percent rise in consumer prices in January, the smallest increase since September, the Labor Department reported yesterday.

The 0.3 percent increase in the consumer price index last month followed increases of 0.4 percent in December and 0.6 percent in November. For the past 12 months, consumer inflation has risen 3.9 percent, slightly above the 3.8 percent pace for all of last year. For the past three months, inflation has risen at a compound annual rate of 5.1 percent, Labor said.

The pace of consumer prices last month was the same as the average monthly increase since the fall of 1981, Labor said.

Gasoline prices fell, before adjustment for seasonal changes, while the costs of meats, poultry and eggs declined in January after seasonal adjustment. Beef prices, which increased 6 percent in the last three months of 1985, fell 0.9 percent last month.

Many economists said that, because the price of a barrel of crude oil has dropped from about $27 a year ago to less than $15 now, inflation will shrink in 1986. However, that improvement may be offset somewhat by the fall in the value of the dollar, which is expected to push up the cost of imported goods and thereby enable domestic manufacturers to increase their prices as well.

Federal Reserve Board Chairman Paul A. Volcker last week warned that the dollar had fallen enough and that further declines could result in accelerated inflation from higher import prices.

The fall of the dollar "will have some effect, but I think it will be overwhelmed by the collapse of oil prices, continued moderation of food prices and global competitive pressures," said Edward Yardeni, chief economist for Prudential Bache Securities.

Yardeni said that, although prices of many Japanese imports are increasing, South Korean firms will sell more cars and video casette recorders in the United States at lower prices, keeping cost pressures on domestic firms and keeping consumer prices down.

Food prices are expected to remain flat for some time, as global oversupplies continue to keep food prices low, Yardeni continued.

American farmers "are going to beg, borrow and steal to plant this season," Yardeni said. "They are trying to pay off debt. I expect another near-record harvest. The real problem with agriculture is there are too many farmers around the world."

Food and beverage costs rose 0.3 percent in January. While the costs of many meats declined, fruit and vegetable prices rose slightly, following virtually no change in December, Labor said. Fresh-fruit prices rose sharply for the second consecutive month, while prices for processed fruits and vegetables maintained their recent nearly stable behavior, increasing only 0.1 percent, Labor said.

Housing costs rose 0.3 percent, the same as in December. Fuel oil prices dropped 1.3 percent, although electricity prices rose 0.6 percent and costs of natural gas increased 0.1 percent.

Gasoline prices fell before seasonal adjustment, but the index for gas at the pump rose 0.1 percent because the decline was not as large as normally occurs this time of year. However, the increase was still small compared with a 1.3 percent rise for the last two months of 1985. Gasoline prices are sill 11.4 percent below their peak of March 1981.

New-car prices rose less in January than in recent months, edging up 0.1 percent, while prices for public transportation, automobile insurance and used cars jumped, Labor said. Used-car prices, which edged up slightly in the previous three months, rose 0.6 percent in January.

In a separate report, the Commerce Department said orders for manufactured durable goods increased a modest 0.4 percent in January despite a surge in orders for military equipment.

Defense orders jumped 45.1 percent, the largest rise in 12 months. Excluding defense, orders would have fallen a sharp 2.8 percent, the Commerce Department said.

Some economists said that, despite strength in other economic indicators, the weakness in the durable-goods report reflected the continued influx of imports of manufactured goods that have offset sales for U.S. factories.