LOS ANGELES (AP) _ ''Tonight Show'' host Johnny Carson has filed suit against his former friend and attorney Henry Bushkin, seeking $16.6 million for repayment of a loan note used to cover a failed real estate development.

The suit, filed Friday in Los Angeles Superior Court on behalf of Carson Tonight Inc., claimed the company purchased the note used to guarantee a loan made to Willowbrook West Ltd., a real estate limited partnership.

Willowbrook's sole asset is a 93-acre parcel of land in Houston, Texas, purchased in 1981 with plans to build a hotel and sell off other lots.

Bushkin represented Carson in several business matters and two of the entertainer's divorces in a professional relationship dating back to the early 1970s. Carson often referred to him as ''Bombastic Bushkin'' in monologues that joked about investment advice from the attorney.

Telephone calls seeking comment were left with both Bushkin's office and that of Carson's new attorney, E. Gregory Hookstratten.

Legal problems stalled the Willowbrook project and were solved only in time for the bottom to fall out of the Houston real estate market.The property remains undeveloped.

Willowbrook's original partners included Carson and Bushkin, two of Bushkin's law partners, playwright Neil Simon and others. The lawsuit names Bushkin law partners Jerry K. Staub and John Gaims as co-defendants.

The lawsuit claimed Carson Tonight purchased the $18.5 million note from United Savings Association in Texas in December of 1986. The 1985 loan was used to ''pay off prior loans and to fund development of and improvements on the property,'' the lawsuit said.

In March, Carson Tonight demanded payment from Willowbrook for the remaining note sum of $16.6 million, the lawsuit contends. Willowbrook failed to pay the sum, the suit alleged.

The document also said the property was to be foreclosed.