A federal law enforcement task force is being set up at the direction of Attorney General William French Smith to coordinate and intensify efforts to prevent fraud in the multibillion-dollar food stamp program.

Smith disclosed formation of the task force during an interview on the ABC News television show "20-20" Thursday night, which alleged that much of the food stamp fraud, which is estimated at as much as $1.5 billion nationwide, involves the use of stolen or forged "authorizations to participate" slips sent to persons eligible to receive food stamps.

The report said that in many instances organized crime is involved in the theft of the authorization slips, a point corroborated yesterday by John V. Graziano, inspector general at the Department of Agriculture.

Graziano's office apparently will continue to play the lead role in the federal anti-fraud effort, but will have additional muscle from other agencies at Attorney General Smith's direction. "Our cases will be addressed with more speed because we will have more people involved," Graziano said.

Organization meetings for the new task force are scheduled for next week, with USDA, the FBI, the Justice and Treasury departments and U.S. Postal Service officials taking part.

During the ABC interview, Smith said, "We now have very strong indications that fraud of the worst kind has permeated the food-stamp program, and we are going to use every effort as quickly as possible to identify those responsible, to prosecute them and put them behind bars."

In reality, Smith's disclosure was not news. Scores of indictments following investigations by the USDA inspector general's agents during the last two years have depicted a clear pattern of criminal abuse and fraud with food stamps.

The new angle, according to Graziano and other USDA officials, is that, for the first time, an attorney general has given a specific order to concentrate federal law-enforcement power on food stamp abusers.

Food stamp officials calculate that the program loses approximately $1.5 billion per year through fraud and abuse and error. "We use 10.2 percent as the error rate, but we can't address how much of that is fraud," Graziano said. "Much of this is based on assumptions and educated guesses."

But, he added, "With approximately 23 million people now taking part in the food stamp program, the opportunity for abuses has grown . . . . Recent indications are that there is escalating interest in food stamps on the part of organized crime."

Data developed by Thomas J. Burke, a deputy assistant inspector general who oversees USDA field investigations, show that during the first nine months of this fiscal year, 450 federal indictments were returned in food-stamp fraud and abuse cases, a pace well ahead of the fiscal 1981 mark.

During the entire 12 months of fiscal 1981, there were 407 food-stamp indictments. Burke said the conviction rate on USDA-based indictments for food stamp fraud is about 90 percent.