Randy Russell and John Ford, key players in the Agriculture Department's negotiations with Congress over the farm bill, will be leaving the administration next month. Both announced their departures last week.

Russell, executive assistant to Secretary John R. Block since January, said he is considering several job possibilities outside of government, although there has been speculation that he will join an agricultural consulting firm started by Richard E. Lyng and William G. Lesher, former top USDA officials.

Russell, a former aide to Sen. Rudy Boschwitz (R-Minn.), joined the department to work on farm legislation in 1981, left in 1982 and returned last year as deputy assistant secretary for economics, working under Lesher.

Ford, a deputy assistant secretary and director of congressional relations, said he is considering work in agriculture-related public relations in this area.

Also leaving the department are Everett Rank, a California farmer who implemented the controversial 1983 payment-in-kind program and is resigning, and Richard A. Smith, a 25-year career bureaucrat who has served during the Reagan administration as administrator of the Foreign Agricultural Service (FAS). He will retire.

Rank was probed during his tenure on his California farm's receipt of an estimated $1 million worth of cotton under the 1983 program that trimmed surpluses by giving farmers crops in return for idling acreage.

Cleared of conflict-of-interest charges, Rank promised to forgo any earnings from the cotton payment, although his partners benefited. He also agreed that his partners would not participate in government programs as long as he was administrator of the Agricultural Stabilization and Conservation Service. His resignation is effective Jan. 2.

Milton Hertz, associate administrator of the agency, is to replace Rank on an acting basis.

Smith has served with the FAS here and abroad and has won the highest awards available to government officials. As of Jan. 24, he is to be replaced by Thomas Kay, current deputy under secretary for international affairs and commodity programs.