Wholesale prices were unchanged in January as a steep decline in energy and food prices offset increases in other products, especially automobiles, the Department of Labor reported yesterday.

At the same time, the Federal Reserve Board reported that industrial production rose 0.4 percent last month. Economists said the increase was consistent with Reagan administration forecasts that the U.S. economy has settled into a period of moderate growth that will continue to create jobs without rekindling serious inflation.

An increase in automobile assemblies to an annual rate of about 8.6 million vehicles a year was the major factor behind the increase in industrial production.

Presidential spokesman Larry Speakes said the two economic reports were part of a "continuing stream of good news that we have had over the last several months indicating the recovery and expansion is in good shape."

Robert Ortner, the chief economist for the Department of Commerce, said that the zero increase overall in producer prices for finished goods was "excellent." But he said that if food and energy are factored out from the index, it rose a "disconcerting" 0.6 percent last month. He said, however, that much of that rise was due to a one-time increase in automobile prices on the first of the year that he does not expect will be repeated.

Wholesale energy prices fell 2.4 percent in January, following a 0.6 percent decline in December. The biggest declines were in gasoline, home heating oil and natural gas prices. Prices of consumer finished foods declined 0.6 percent. On the other hand, the prices of passenger cars rose 2.2 percent last month. Monthly price changes are adjusted to account for seasonal variation.

Ortner noted that the freeze that devastated many of the nation's winter fruit and vegetable growing regions will likely trigger an increase in some food prices that could show up in the producer price report for February. Overall, however, he said, price increases -- at both the producer and consumer levels -- should remain moderate for 1985. Inflation at the producer level rose 1.8 percent in 1984 and 0.6 percent in 1983 -- the smallest two-year increase since 1963 and 1964.

Prices of so-called finished producer goods -- those that need little further processing before their final sale -- do not translate directly into consumer prices, because consumers buy services as well as products. However, stable producer prices are an indication that overall consumer prices will rise at a moderate level.

Prices of intermediate goods -- such as components, construction materials and crude vegetable oils -- declined 0.1 percent in January, while unfinished goods fell 2.2 percent.

A variety of factors are acting to keep inflation at its lowest level in more than a decade, including moderate economic growth that keeps demand at a level that does not trigger shortages and bottlenecks; increasing capacity; firm monetary policy, and the strong U.S. dollar.

The high-priced dollar keeps the cost of many imports low -- both commodities that are the beginning of the production chain and finished goods that compete with U.S. products. Slower economic recoveries in most of the rest of the world encourage foreign producers to export their lower-priced goods here, rather than sell them at home. The slower worldwide growth also helps keep down demand for oil products, contributing to the continuing price decline in petroleum products.

Jerry Jasinowski, chief economist for the National Association of Manufacturers, said the strong U.S. dollar probably knocks between 1.5 and 2.5 percentage points off the U.S. inflation rate.

Jasinowski said the 0.4 percent increase in industrial production -- following a revised 0.5 percent rise in December and a 0.4 percent increase in November -- is consistent with overall economic growth at a roughly 3.5 percent annual rate in the first three months of 1985.

"That doesn't represent a boom but does show solid economic growth," Jasinowski said.

January industrial production -- which is only a portion of the overall output of goods and services in the U.S. economy -- was dominated by a steep rise in automobile assemblies. In other areas, the increase in output was more modest.

Seasonally adjusted, manufacturing production rose 0.2 percent in January, compared with 0.8 percent in December; production of business equipment rose 0.3 percent, compared with 1.3 percent in December, while output of materials increased 0.4 percent after rising 0.1 percent in December.