New York — Two of the country’s best-known investors, Warren Buffett and Laurence Tisch, have sold shares in Champion International Corp., a paper producer with a plant in Bucksport, at high prices.

Buffett got $49.13 for his shares; Tisch got $52.45. A week ago, Champion International stock traded at $54.50, its all-time high and double what it was three years ago.

The buyer of most of these shares was Champion International itself.

All sides may have benefited. Buffett’s sale brought him a total return of 80 percent for five and a half years on the money he had invested in Champion.

Tisch chalked up a capital gain of about $145 million and still let the bulk of his bet on Champion ride. Champion International, rolling in profits because of the strong U.S. economy, reduced its shares outstanding by 10 percent, increasing its prospects for earnings-per-share gains in the years ahead.

A week ago Thursday, Champion said it had bought 7.89 million shares from Buffett-controlled Berkshire Hathaway Inc. for a total of $388 million. Buffett got the stock by converting 300,000 shares of Champion preferred stock he bought in December of 1989.

Buffett paid $300 million for the preferred, which paid $27.75 million a year in dividends. That means the investor had a total return of about $241 million — $88 million in trading profit and $153 million in dividends.

Loews Corp., controlled by Tisch and his family, this week sold 5.5 million Champion shares in a public offering, still hanging onto about 9 million shares. Champion bought 2 million of the shares offered. Tisch’s company bought the shares over a long period, paying an average price of about $26 a share.

By buying stock back from its two big shareholders, Champion prevented an instant dilution of its per-share earnings and helped support the share price in the market.

The company also is improving its balance sheet. Champion said this week that it will redeem convertible bonds with a face value of $150 million. The company said that by the end of the year its total debt as a share of capital will be down to 38.6 percent from 43.5 percent at the end of last week.

Champion clearly benefits from the runup in demand for paper. Prices for the kind of paper used in copiers and laser printers rose 11 percent in the second quarter, Merrill Lynch & Co. analyst Sherman Chao said. The price of the paper used in newspapers and telephone books has jumped 65 percent since early 1994.

The question is how long the boom, now a year old, will last. Most industry analysts think awhile. The average estimate for Champion International’s 1995 earnings is $6.76 a share, compared with 9 cents in 1994.