CHICAGO (AP) _ UAL Corp. announced Thursday it has made peace with its largest shareholder, Coniston Partners, which had threatened to oust directors of the United Airlines' parent unless a union-led buyout was approved.

Under the agreement, two officials from the New York-based investment firm will join the 13 current members on UAL's board. In return, Coniston promised not to take part in any takeover attempt of UAL for at least the next 2 years, UAL said in a statement.

Chicago-based UAL also agreed to repurchase up to 2 million shares of its stock to improve shareholder value.

UAL stock, which peaked at $296 last year, closed Thursday on the New York Stock Exchange at $94.75, up $5.

In November 1989, Coniston acquired 2.5 million shares, or 11.8 percent of UAL stock, for an average disclosed price of $161 a share. Faced with paper loses of $100 million, Coniston this spring was threatening a proxy fight with the UAL board.

Last week, the union's failed to make a deadline for financing a $201 per share, $4.4 billion buyout offer. The UAL board rejected other offers the unions presented.

''By putting the uncertainty over ownership behind us, we can move forward to focus our full attention on United's long-term strategic plan and industry opportunities as they arise,'' said Stephen M. Wolf, UAL's chairman and president.

Paul E. Tierney Jr. - who was appointed to the UAL board from Coniston along with Keith R. Gollust - said he thought the deal was good for stockholders.

''In consideration of worldwide economic conditions, including the price of oil, working with management and the board will produce the greatest value for shareholders,'' he said in the UAL statement.

Coniston officials did not immediately return telephone calls Thursday evening.

Financial analyst Stephen Dexter of Kemper Financial Services Inc. in Chicago said UAL officials ''are getting rid of the biggest thorn in their side, dealing with takeover threats and at the same time, doing something for their stockholders who have suffered all the pain in recent months.''

Dexter said the agreement will make contract talks more difficult for employees.

''Coniston, once an ally, is now part of the establishment,'' he said.

Spokeswoman Bobbie Pilkington of the Association of Flight Attendants said UAL had not notified union leaders and her union could not comment.

Earlier in the day, the three major unions at United Airlines said they are banding closer together so they can fight any company attempts for concessions in upcoming contract talks.

More than 80 leaders of unions representing pilots, flight attendants and mechanics met Wednesday in Chicago.

''The purpose of this summit was to discuss strategies in preparation for the resumption of traditional contract bargaining with United Management,'' they said in a statement.

''It was generally determined that in light of Mr. Wolf's record of aggressive concessionary bargaining tactics, labor at United must continue to mature (their) alliance,'' they said in the statement.

The leadership of the three unions agreed to establish ''The United Employee Coalition'' to assist each other in their bargaining goals.

UAL declined comment on the union statement, said spokesman Joe Hopkins.

Some observers say the company needs concessions from the unions to meet its expansion goals. Unions say they are looking for major improvements in wages and benefits, and some think there's a potential for a major national labor dispute.

Negotiations could be soured by a bitterness from the unions' failed seven- month effort to buy UAL. Suspicions that Wolf tried to undermine the buyout have worsened anti-management sentiments.

All of United's 47,300 union employees, comprising about two-thirds of UAL's labor force, are working under extended contracts.

No dates have been set for talks, and the earliest they're expected to begin is the first weeks of November.