A federal appeals court Monday agreed to let the NFL extend pro football’s lockout, allowing team owners to keep the sport shut down while they appeal a lower court ruling that ordered them to resume normal operations.

The decision is a significant victory for the league, because it could prolong the lockout for weeks or months beyond a scheduled June 3 hearing on the merits of the case. Such delays put increasing pressure on the players’ side in collective bargaining negotiations.

“We have serious doubts that the district court had jurisdiction to enjoin the league’s lockout, and accordingly conclude that the league has made a strong showing that it is likely to succeed on the merits,” a 2-1 majority of the three-judge appellate panel concluded.

With the lockout imposed by team owners March 12 in place, teams are prohibited from signing free agents or trading players. Coaches are not permitted to have contact with players. The sport’s drug-testing program is not in effect.

And the sport’s first work stoppage since 1987 moves closer to forcing the postponement or cancellation of games. Training camps normally would open in late July or early August.

The three-judge panel of the Court of Appeals for the Eighth Circuit that ruled Monday evening previously had granted the league’s request for a temporary stay of federal Judge Susan Richard Nelson’s April 25 injunction, which temporarily lifted the lockout. Hours after the temporary stay was granted, the NFL again barred players from team facilities after some of them had spent a single day there under guidelines issued by the league.

In Monday’s decision, two judges, Steven M. Colloton and Duane Benton, agreed to keep the lockout in place. The third judge, Kermit E. Bye, dissented. The judges had divided along the same lines on the temporary stay.

Bye is a Democratic appointee. Colloton and Benton are Republican appointees.

In his dissent, Bye wrote that “due to the irreparable harm presently incurred by the players, compared with the limited harm, if any, suffered by the NFL, I believe the balance of harms weighs heavily in the players’ favor.”

James Quinn, an attorney for the players, said Monday’s decision was “no surprise. We fully expected the stay to be extended until the appeal is heard on June 3 in St. Louis.”

In a statement, the NFLPA wrote: “The NFL’s request for a stay of the lockout that was granted today means no football. The players are in mediation and are working to try to save the 2011 season. The court will hear the full appeal on June 3.”

Greg Aiello, the NFL’s senior vice president of public relations, said in a written statement that “it is now time to devote all of our energy to reaching a comprehensive agreement that will improve the game for the benefit of current and retired players, teams, and, most importantly, the fans. This litigation has taken the parties away from the negotiating table where these issues should be resolved.”

If the two sides don’t reach a negotiated agreement, it is difficult to predict how long the overall court process could take. But legal experts have said the court could take weeks, or longer, to rule after it holds the hearing June 3.

In appealing Nelson’s decision to the higher court, the NFL argued that it would suffer irreparable harm without a stay of the injunction granted by Nelson, in part because free agent players would begin signing with teams while the league’s appeal is still being considered in court. The players’ side urged the appeals court to retain Nelson’s lifting of the lockout.

The league contends that Nelson brushed aside key legal arguments made by the NFL. Nelson rejected the league’s arguments that federal labor law prohibited her from granting an injunction in a labor dispute; that she should wait for the National Labor Relations Board to complete a separate investigation; and that the league should be shielded from antitrust claims by the players because the players’ decertification of their union is not valid.

One day before the owners locked out the players on March12, the players dissolved their labor union, the NFL Players Association, and filed an antitrust lawsuit against the owners. Attorneys for the players argued the lockout is illegal under antitrust laws in the because the players no longer are represented by a union.

Representatives of the league and the players also resumed mediated talks Monday in Minneapolis under the oversight of Chief Magistrate Judge Arthur J. Boylan. Boylan mediated four days of meetings before the talks recessed.