Americans have dramatically increased the use of wood to heat their homes over the past few years, according to the Energy Department's first major study of wood energy consumption.

A related report found that 5.5 percent of American homes used wood as their primary source of heat in 1981. Wood fuels now generate about the same amount of residential energy as nuclear power plants, according to R. Gene Clark, director of DOE's division of nuclear and alternate fuels.

Between 1974 and 1981, spurred by higher prices for fossil fuels such as coal, oil and natural gas, Americans increased their overall use of wood as a fuel by 45 percent and as a residential fuel by 113 percent. Wood-fuel use had declined steadily from 1949 to 1974 for utilities, residences and commercial businesses, although industrial use had increased steadily over that period, the report found.

In Virginia, residential use of wood fuels increased 148 percent from 1974 to '81; in Maryland, it increased 129 percent, and in the District, 114 percent.

Among the conclusions of the 18-month study:

* Industry uses 62 percent of the wood fuel, primarily to power paper and timber mills. The report said that industry interest in wood has been revived, in part, by the "implementation of environmental regulations" that limit the burning of fossil fuels. But the report said that, because of the downturn in the economy last year and its impact on the timber and housing industries, there would be "lower production levels and less wood energy consumption" in the short term.

* Thirty-seven percent of wood fuels are used in homes. Household use declined in the 1950s and 1960s primarily because other fuels were "abundant, cheap and more convenient." Rising costs of oil and gas and the disruption of crude oil supplies then revived interest in wood.

* About 0.7 percent of wood fuels are used in commercial buildings and less than one-tenth of a percentage point in utility plants. In 1981, utilities relied on wood in only three states -- Vermont, Montana and Wisconsin.

Today, the report states, nearly 81 million tons of wood are used annually to provide energy, three times the amount that the nation used in 1949.