1990 after Mrs. Marion MacMillan's US attorney worried that the heiress would lose money on the sale, Supreme Court was told yesterday.

The wealthy heiress to a grain fortune wants to back out of a $8.5-million agreement she later signed to sell the island to Canadian businessman Mr.

Michael DeGroote.

Government Senator Jerome Dill of Appleby, Spurling and Kempe, Mrs.

MacMillan's former lawyer, testified the island was listed at $6.5 million in November of 1989.

But in January of 1990, Mr. Dill said he received a telephone call from Mr.

Bob Engel, Mrs. MacMillan's US lawyer and financial adviser.

Mr. Engel was concerned if Mrs. MacMillan sold the island retreat in Riddell's Bay for $6.5 million, "she would break even, or might have a small loss.'' In February, Mr. Dill sent a notice to realtors who had the listing, advising them the price was to be hiked to $7 million, he said.

Mrs. MacMillan, 60, is a member of the family which owns Cargill, America's biggest private company. She is said to be worth $700 million.

She bought Perot's Island in 1987, and the court has heard she spent up to $3 million on renovations to the house and its surroundings.

In December of 1990, Mrs. MacMillan signed an agreement to sell the island to Mr. DeGroote, a Canadian multi-millionaire who formerly headed the waste and transportation giant Laidlaw.

Mrs. MacMillan changed her mind after therapy classes, run by Mrs. Sarah White, began meeting on Perot's Island.

Mr. DeGroote wants her to stick to the deal, and has gone to court to try to seal his claim.