WASHINGTON -- Three years ago, U.S. Department of Agriculture employees determined that synthetic additives in organic baby formula violated federal standards and should be banned from a product carrying the federal organic label. Today, the same additives -- purported to boost brainpower and vision -- can be found in 90 percent of organic baby formula.

The government's turnaround, from prohibition to permission, came after a USDA program manager was lobbied by the formula makers and overruled her staff. That decision and others by a handful of USDA employees, along with an advisory board's approval of a growing list of non-organic ingredients, have helped numerous companies win a coveted green-and-white "USDA Organic" seal on an array of products.

Grated organic cheese, for example, contains wood starch to prevent clumping. Organic beer can be made from non-organic hops. Organic mock duck contains a synthetic ingredient that gives it an authentic, stringy texture.

Relaxation of the federal standards, and an explosion of consumer demand, have helped push the organics market into a $23 billion-a-year business, the fastest growing segment of the food industry. Half of the country's adults say they buy organic food often or sometimes, according to a survey last year by the Harvard School of Public Health.

But the USDA program's shortcomings mean that consumers, who at times must pay twice as much for organic products, are not always getting what they expect: foods without pesticides and other chemicals, produced in a way that is gentle to the environment.

The market's expansion is fueling tension over whether the federal program should be governed by a strict interpretation of "organic" or broadened to include more products by allowing trace elements of non-organic substances. The argument is not over whether the non-organics pose a health threat, but whether they weaken the integrity of the federal organic label.

Agriculture Secretary Tom Vilsack has pledged to protect the label, even as he acknowledged the pressure to lower standards to let more products in.

In response to complaints, the USDA inspector general's office has widened an investigation of whether products carrying the label meet national standards. The probe is also looking into the department's oversight of private certifiers who are hired by farmers and food producers and inspect products to determine whether they can use the label.

Some consumer groups and members of Congress say they worry that the program's lax standards are undermining the federal program and the law itself.

"It will unravel everything we've done if the standards can no longer be trusted," said Sen. Patrick Leahy, D-Vt., who sponsored the federal organics legislation. "If we don't protect the brand, the organic label, the program is finished. It could disappear overnight."

Organic advocates and food marketing experts said the introduction this month of new "natural" products by an organics division of Dean Foods is the latest sign that the value of the USDA label has eroded. The yogurt and milk products will be distributed under the Horizon label and marketed as a lower-priced alternative to organic products.

Congress adopted the organics law after farmers and consumers demanded uniform standards for produce, dairy and meat. The law banned synthetics, pesticides and genetic engineering from foods that would bear a federal organic label. It also required annual testing for pesticides. And it was aimed at preventing producers from falsely claiming their foods were organic.

The USDA created the National Organic Program in 2002 to implement the law. By then, major food companies had bought up most small, independent organic companies. Kraft Foods, for example, owns Boca Foods. Kellogg owns Morningstar Farms, and Coca-Cola owns 40 percent of Honest Tea, maker of the organic beverage favored by President Barack Obama.

That corporate firepower has added to pressure on the government to expand the definition of what is organic, in part because processed foods offered by big industry often require ingredients, additives or processing agents that either do not exist in organic form or are not available in large enough quantities for mass production.

Tom Harding, a Pennsylvania-based consultant for small local farmers and big producers, including Kraft, said broadening the law has helped meet demand by multiplying the number of organic products and greatly expanded the amount of agricultural land that is being managed organically. "We don't want to eliminate anyone who wants to be a part of the organic community," he said. "The growth we've seen has helped the entire organic food chain."

Under Barbara Robinson, who administers the organics program and is a deputy USDA administrator, the National Organic Program has repeatedly opted not to issue standards spelling out how organic food must be grown, treated or produced.

In 65 instances since 2002, the standards board has made recommendations that have not been acted upon, creating a haphazard system in which the private certifiers have set their own standards for what products can carry the federal label.

Ms. Robinson has blamed the delays on the program's small staff, saying, "We have to prioritize."

Consumer groups and organics advocates are hopeful that the Obama administration will bolster the program. In his proposed budget, the president has doubled resources devoted to organics and installed USDA leaders who support change.

Mr. Vilsack's deputy, organics expert Kathleen Merrigan, told consumer groups three weeks ago that she intends to heighten enforcement. She helped write the original organics law and get the program off the ground in 2002.