Santa Fe Southern Pacific Corp. yesterday repurchased 6.657 million shares of its own stock at a price of 25 3/8 in the fourth-largest trade in New York Stock Exchange history in terms of number of shares.

The $168.9-million transaction, handled by Salomon Brothers Inc., was the eighth-largest Big Board trade in dollars. Santa Fe Chairman John J. Schmidt said the purchase was part of a plan the company announced in June to repurchase up to 10 million shares of its common stock.

Santa Fe has approximately 190 million common shares outstanding.

The largest number of shares traded as a block on the NYSE was the 10 million-share purchase of Superior Oil Co. stock by Mobil Corp. in June for $423.7 million. Mobil recently completed the purchase of Superior Oil in one of the largest oil mergers this year.

The second-largest number of shares in a single transaction was the sale of 7 million shares of American Express Co. stock by Financial Corp. of America in August for $223.7 million.

Santa Fe was the most active stock on the NYSE yesterday, closing at 25 1/4, down 1/8, on total turnover of 7 million shares.

Santa Fe is a transportation and natural resources company formed last December through the merger of Santa Fe Industries and Southern Pacific Co. The combination of the two companies' rail operations would create the nation's third-largest rail system if approved by the Interstate Commerce Commission.

Southern Pacific Transportation Co. is currently held in trust pending a ruling by the government on the combination.