Phillips Petroleum Co., which is trying to sell $2 billion in assets to reduce its huge debt, said yesterday that potential buyers have expressed a strong interest in buying properties it values at between $800 million and $900 million.

When added to the $53 million in assets already sold and contracts to sell another $87 million, the sales are "progressing as planned," said spokesman Dan Harrison.

The nation's eighth-largest oil company increased its debt by $4.5 billion earlier this year to pay for a stock repurchase program that rescued it from two hostile takeover bids. It had assets of $16.965 billion as of the end of 1984.

Harrison said Phillips, based in Bartlesville, Okla., is continuing to examine its "basket of assets" to decide what else to put on the market. He said the prospective purchasers are "people that are definitely interested in pursuing talks and seeking information," but said it would be premature to identify them.

"We feel that we are going to be close on selling $1 billion worth of assets by year end, which is a schedule that we have set for ourself," Harrison said. "We expect sometime later to identify additional assets that would be on the market. This is a process that certainly does not happen overnight."