The Agriculture Department will approve for broad use tomorrow a genetically modified soybean engineered to contain healthier oils, the opening salvo in a biotech oil fight between DuPont Co. and its rival, Monsanto Co.

The high-oleic soybean, developed by DuPont and pending deregulation since 2006, is one of the first in a wave of bioengineered cash crops that are being altered for nutritional purposes. Currently, nearly all biotech crops grown in the United States have been altered for resistance to weedkiller or insects, traits that are rarely felt by consumers or commercial businesses.

The USDA deregulation is the “final step” in the approval process for Dupont’s soybean, which has already been approved in Canada and Mexico, said Bridget Anderson, a spokeswoman for Pioneer Hi-Bred, DuPont’s biotech seed business. The crop and its oil will continue commercial testing this year and should be ready for global use by 2012, she added.

The USDA approval is also the first play in a coming oil war between DuPont and Monsanto.

Currently, Monsanto has two varieties of biotech soybeans pending approval with USDA that also seek to modify the nutritional value of soybean oil, promising to eliminate trans fats and produce oil with omega-3 fatty acid — fish oil — for use in yogurt, granola bars and spreads.

The modified soybeans represent a move by DuPont and Monsanto to broaden the crop traits engineered in their seeds beyond simple properties like pest resistance to complex areas — like nutritional value, drought tolerance and nitrogen fixation — that are often influenced by multiple genes. These long-promised traits previously found little purchase in the seed giant’s business plans.

It is “pretty exciting science,” said Rob Fraley, Monsanto’s chief technology officer. Leveraging improvements in breeding and biotechnology, he said, seed giants like Monsanto “can start to take on some of the most complex physiological traits in terms of crop quality and health and nutrition.”

DuPont’s biotech soybean could be welcome news for soy farmers, who have seen food companies move away from standard soybean oil as they work to eliminate trans fats, which are linked to coronary health risks, from their ingredients. It is a difficult shift. The industry uses about 6 billion pounds of the oil each year, all of which contained trans fats.

The biotech soy will provide a stable oil alternative that can be used without hydrogenation, the process that creates trans fats, DuPont said. The oil has already been tested successfully for snack food preparation for frying or spraying, according to DuPont.

Notably, the engineered soybeans have been created through a different process than most biotech crops on the market, which contain splices of bacterial genes to grant herbicide or pest resistance. Instead, DuPont scientists “silenced” the expression of a gene in the fatty acid pathways of the soybean seeds. Few commercial biotech crops have used gene silencing so far, with a virus-resistant papaya in Hawaii being a notable exception.