Baseball commissioner Bowie Kuhn testified in court today that, shortly before Charles O. Finley tried to sell three of his Oakland A's players for a total of $3.5 million, Finley was warned that any sale might be canceled by Kuhn if the price tag was $1 million.

Kuhn was composed and assertive as he was cross-examined in U.S. District Court, where Judge Frank J. McGerr is hearing Finley's $3.5 million suit against the commissioner for voiding the sales last June.

The taking of testimony ended after 15 days and McGarr asked attorneys for Kuhn and Finley to file posttrial briefs by Feb. 28. The judge said he would try to make a ruling as soon as possible after reading them.

McGarr also dismissed the Boston Red Sox and the New York Yankees as codefendants in the case. He added that he would not order the Red Sox, who were in line to get Rollie Fingers and Joe Rudi for $1 million each, or the Yankees, who were scheduled to obtain Vida Blue for $1.5 million, to pay Finley if he should win the case.

Kuhn answered affirmatively when Finley attorney Neil Papiano asked if he had made any attempt, directly or indirectly, to warn Finley that the sale of player contracts for substantial sums might be disapproved.

Kuhn said he called Lee S. MacPhail, president of the American League, and said, "I don't know all the details but I understand Mr. Finley is going to try to sell some players for $1 million and that would cannibalize his team. You better talk to him. Mr. MacPhail said, "I tried to and he hung up on me."

Papiano also tried to establish that Kuhn had arbitarily used the Oakland club as an instrument to hasten collective bargaining on a new, modified reserve system with a re-entry draft for free agents when he voided the sales.

"I believed voiding them would help develop a re-entry system to preserve competitive balance," Kuhn replied, but pointed out that it was Finley who created the circumstances that prompted him to act and that he had not singled out Oakland as a tool.

Papiano also asked if here were any policies on not trading or selling players who were playing out their options while the new contract was being negotiated.

Kuhn said such a policy was "implicit" in papers sent to the clubs by the player relations committee, the owner's bargaining agent.

"There is no reason in the world Mr. Finley shouldn't have known that," Kuhn answered."He and he alone went outside the system."

The commissioner was asked what information about his conversations with Finley he had passed in a telephone conference call with the executive council, an advisory body to the commissioner.

Kuhn said he was not sure he mentioned that Finley had complained of serious financial problems with his club and insurance business. He also said he did not tell them Finley thought other players on the team could replace the ones he sold but did mention that Finley said he planned to use some of the money to rebuild the club.

When asked how else Finley could have recouped on the investment he had made in his players over the years if they were to become free agents at the season's end, Kuhn replied:

"He had already had his players for many years and they had done very well. So I think it's fair to say he had recouped on his investment."

He added that Finley could possibly have received money for them in a waiver deal or tried to sell them at the end of the season to a Japanese club. but described the latter as being "not very realistic."

The commissioner said he relied on his own ability to judge the caliber of the three players whose loss to the A's he believed would further weaken the club and take it out of competition in midseason in the American League's West Division race.

After establishing that Kuhn kept no fields on the talent of baseball's 600 major league players, Papiano contended the commissioner was unqualified to judge the talent of any players.

On a question about his powers, Kuhn said he did not believe he had the unilaterral right to make baseball rules but could revoke them.