American Telephone and Telegraph Co. Announced the negotiated sale of $600 million of 10-year notes, due June 1, 1990. The interest rate of the notes is 10 3/8 percent.

AT&T, which last went to the debt market in 1975, said it intends to use the proceeds for equity investment in subsidiary and associated companies and for general corporate purposes.

Coca Cola Co., meanwhile, informed the Securities and Exchange Commission yesterday it plans to sell $100 million in bonds, its first entry into the public debt market since 1920.

A company spokesman said the bonds, to mature in 1985, are being sold to pay off short-term debts.

"We are obviously still a very strong and financially conservative company," said Jack Stahl, a spokesman for the treasurer's office. "But we have needs for moderate amounts of debt, particularly on a seasonal basis."

Stahl said the company thought the recent drop in interest rates gave it the opportunity to substitute moderate term debt for the short term debt carrying higher interest charges.

Coca Cola, the world's largest manufacturer and distributor of syrups and concentrates for soft drinks, incurred the debts by buying companies that owed about $36 million.