WASHINGTON (AP) _ Rice farmers will soon get about $580 million as final payments for participating in the 1990 rice program, the Agriculture Department said Friday.

Keith Bjerke, executive vice president of the Commodity Credit Corp., said the cash payments will be made at county offices of the Agricultural Stabilization and Conservation Service.

Advance payments totaling $220 million were made upon request when rice farmers signed up in last year's program.

The ''deficiency payments'' are made to bridge the gap between a target price and the actual market price received by farmers or the loan rate, whichever is higher.

Officials said the five-month market average used in the program was below the loan rate, so the loan rate of $6.50 per hundredweight was used to compute the payments. The target was $10.71 per hundredweight.

The loan rate, or price support loans, indicate how much farmers can borrow from USDA using their crops as collateral.