WASHINGTON – American farmers will plant more genetically engineered crops this year, including one-third of the corn on U.S. soil, shrugging off international resistance to biotech food.

The farmers are expected to grow more than 79 million acres of genetically engineered corn and soybeans, the nation’s two most widely planted commodities, a 13 percent increase from last year, according to the Agriculture Department’s spring survey.

The gene-altered crops require fewer chemicals, making them easier and cheaper to grow. The crops are engineered to be toxic to insect pests or to be resistant to a popular weedkiller.

“Farming has become so competitive, so small margin, that if we can find something that works economically and environmentally we’ll jump on it,” said Minnesota farmer Gerald Tumbleson, who grows biotech corn and soybeans.

About 74 percent of this year’s soy crop, or 54 million acres, will be genetically engineered, compared with 68 percent last year and 54 percent in 2000, the department said Thursday. Soy is a critical ingredient for a wide variety of foods and, like corn, also is used for animal feed.

Some 32 percent of the corn crop, or 25.3 million acres, will be of biotech varieties, compared with 26 percent in 2001 and 25 percent the year before.

Strong consumer resistance to agricultural biotechnology has arisen in Europe and Japan, but most U.S.-grown corn and soy is used domestically.

“The farmer looks at it strictly from profitability,” said commodities analyst Don Roose. “They’re not shying away from it.”

About 10.5 million acres of cotton, or 71 percent of this year’s cotton crop, will be bioengineered. Last year, 69 percent of the cotton was gene-altered.

The corn and cotton are considered better for the environment because they reduce the use of insecticides.

The biotech soybeans save farmers time. The crop contains a bacterium gene that makes the soybeans immune to Roundup herbicide. To control weeds in conventional soybeans, farmers must either cultivate more often or spray their fields more frequently with less powerful weedkillers. Critics are concerned Roundup is being used so much that weeds will develop resistance to it.

In Nebraska, South Dakota, Kansas and Indiana, 80 percent or more of the soybean crop is expected to be biotech.

The popular varieties of biotech cotton are either Roundup-immune or else produce their own pesticide. Most of the genetically engineered corn that farmers plant was designed to kill a common insect pest, the European corn borer.

The crops were first commercialized in the mid- to late 1990s, and the Agriculture Department has surveyed their use nationally since 2000.