The Justice Department has decided that there are no grounds to prosecute Everett G. (Bud) Rank Jr., an Agriculture Department official whose farm obtained more than $1 million from a federal subsidy program he directed.

But Justice's Public Integrity Section, after reviewing a lengthy investigative record compiled by USDA's inspector general, indicated that it was troubled by Rank's involvement and said that USDA should act to see that Rank does not violate conflict-of-interest law in the future.

Agriculture officials said that ethics "orientation sessions," apparently much like police traffic school, have been started for all USDA executives and that Rank will be assigned to attend one of the classes.

Rank had been cleared earlier of conflict-of-interest charges related to his farm's participation in the 1983 payment-in-kind (PIK) program that he oversaw as head of the Agricultural Stabilization and Conservation Service (ASCS).

But the case was reopened last year after a California television station reported that he might have given favorable PIK program treatment to Calcot, a cooperative that marketed his farm's cotton. Rank's telephone logs showed extensive contact with Calcot officials when critical PIK decisions were being made.

Gerald E. McDowell, head of the Public Integrity Section, told USDA officials last month that Justice had decided it could not prosecute Rank because of several other "equitable and practical considerations." Among them, he said, was a finding that Rank might not have been counseled adequately about conflict-of-interest rules.

The administration's handling of the Rank case drew a sharp reaction from Rep. Fortney H. (Pete) Stark (D-Calif.), who in the past had criticized large payments to wealthy farmers, including Rank and his partners, through the PIK program.

"It looks like the administration is not bothering to prosecute another senior official," Stark said. "The only thing USDA is making Bud Rank do is attend an ethics class. I'm tired of 50-year-old men in this administration having to take on-the-job courses in ethics."

Rank, a Californian who became head of the ASCS in 1981, was admonished by John J. Franke Jr., assistant secretary of agriculture for administration, in a letter earlier this month. Franke warned that Rank should be more careful to avoid "even the appearance of a conflict of interest."

"The highly visible and politically sensitive nature of your position makes it critically important that you exercise care in all your actions," Franke wrote.

After The Washington Post disclosed in 1983 that the Fresno County farm in which Rank is a partner obtained surplus federal cotton worth about $1.2 million through PIK, the ASCS administrator denied knowing that his associates had enrolled the farm in the program. Rank said he took no part in the farm's business decisions after taking the ASCS job.

The Fresno County operation, Cinco Farms, received the cotton in return for agreeing not to plant a crop that year as part of the government's effort to reduce commodity surpluses and boost farm prices.

The investigative report quoted J. Michael Kelly, a USDA ethics adviser, as saying that Rank was puzzled about the conflict-of-interest allegations.

"He does not appear to accept or comprehend that his 17 percent ownership interest in Cinco could have been enhanced to the extent of 17 percent of the income from PIK," Kelly said.. CAPTION: Picture, Everett G. (Bud) Rank Jr . . . .his farm obtained $1.2 million.