Citicorp yesterday filed suit in U.S. District Court here against the Interbank Card Association, the company that issues Master Charge and Interbank credit cards, to prevent it from going into the travellers check business on the grounds that it would be anticompetitive.

Citicorp, through a subsidiary, now has about 20 percent of the U.S. travelers' check market with its First National City checks. It chasged that Interbank's plan to issue travelers checks with a Master Charge logo through its network of 8,000 member banks and savings institutions would ultimately result in that check's illegal domination of the $10 billion U.S. market.

Officials of Interbank could not be reacned for comment on the antitrust suit.

Interbank has recently organized MCTC Corp. To issue, distribute and sell travelers' checks through its banking network that serves as the payment system for Master Charge.

"Consumer purchases of travelers' checks, ordinarily do not have a strong type or brand preference," Citicorp claimed in its suit. It said it be lieves that "approximately 90 per cent of them will accept whatever travelers' check is put before them by a selling agent bank.

"This fact and the method by which travelers' checks are sold confers upon the selling institutions, including Interbank member banks and MCTC member banks, the power to favor one travelers' check purchased," the suit continued.

Citicorp noted that of the 8,000 Interbank members, approximately 3,500 banks currently act as selling agents for First National City travelers' checks. During 1977 they sold approximately $1 billion of its checks. Citicorp expressed fear that if Interbank went ahead with its plans. Citicorp would lose these outlets for its travelers' checks.

Citicorp's 20 percent share of the U.S. travelers' check market puts it in second place, well behind American Express with a 60 percent share. Third is BankAmerica Corp. with 15 percent. The remaining 5 percent is presently divided among Barelays, Republic and Thomas Cook, according to the suit.

(Special correspondent John Kennedy contributed to this story.)