A conflict-of-interest investigation into the activities of Agriculture Department official Everett G. Rank has been reopened on orders from Secretary John R. Block, after new reports of Rank's role in the 1983 payment-in-kind (PIK) program.

The probe is being conducted by the USDA's inspector general, who last year cleared Rank of conflict charges after it was learned that a farm in which he was a partner had received free federal cotton worth about $1 million in the PIK program that he helped design and administer.

Rank insisted that he did not know that the Fresno County, Calif., farm had been enrolled by his partners in the PIK program. He promised that the farm would not take part in federal farm programs as long as he remained chief of the Agricultural Stabilization and Conservation Service.

New questions about Rank's handling of the PIK program were raised earlier this month by KRON-TV in San Francisco, which obtained the USDA official's telephone and appointment logs through a Freedom of Information Act request. Block ordered that the case be reopened after viewing the station's report, sources said.

Rep. Fortney H. (Pete) Stark Jr. (D-Calif.), an early critic of Rank and the cotton PIK program, said yesterday that "major unanswered questions" remain and that he still believes that Rank's share of the farm's PIK profit should be returned to the government, rather than to Rank's partners.

Although Rank said he had had no contact with his farm operation since he came to Washington in 1981, logs showed that he had had more than 20 telephone conversations with the farm manager and his partners. The farm manager told USDA investigators he had had no contacts with Rank.

The logs indicated a series of meetings between Rank and cotton industry representatives when the PIK program was being designed. KRON-TV also said that the logs showed contacts between Rank and officials of Calcot, a cooperative to which his farm belonged, and that Calcot was allowed to sell surplus cotton when the USDA had frozen all supplies to ensure adequate amounts for farmers participating in PIK.

Rank acknowledged meeting with Calcot officials while the PIK program was being set up, but denied having shown favoritism.