The National Football League strike, which appeared to be close to a settlement earlier today, reached another stage of acrimony late this evening, with the head of the players' union calling a press briefing at which he attacked management for what he called a "classic case of union busting.

"At this point, we are not even close" to a settlement, said Ed Garvey, executive director of the NFL Players Association. At his news conference at 11:30 p.m., he said: "We have called this meeting to counter a flood of misinformation put out by the management council to the effect that a settlement would be reached. We are nowhere near an agreement. The management council took away many of the benefits which they had had on the table."

The sides had resumed contract talks through an intermediary and there were reports earlier today that management was reworking the language of its last offer to meet objections raised by players.

What had appeared to be a breakthrough in the negotiations came after the National Labor Relations Board rejected seeking an injunction against the owners, accused by the union of bargaining in bad faith.

Paul Martha, who, it was learned, has been serving as an intermediary in indirect talks since Saturday, said this evening he hoped to have the sides back together in 24 hours. "It is up to each side what they can agree on," he said.

The union's representatives accused the league of taking back concessions it already had agreed to informally. Among these, said the union, were performance incentive bonuses, a roster size of 49 instead of 45 and reinstatement with full back pay for three player reps who had been cut from their teams. The union said management also had reduced an earlier offer covering severance pay.

When the talks ended tonight, the 56th day of the strike, the status of negotiations appeared clouded.

All this followed a day of optimistic reports in which some managment sources had said a settlement was possible in time for play to be resumed Sunday.

It was learned that if that happened the league planned on resuming the season with Sunday's games and the games not played because of the strike probably would not be made up. Six weeks of games remain to be played.

The top eight teams in each conference would take part in three weeks of playoffs to determine the Super Bowl participants. The Super Bowl would be played as scheduled, Jan. 30.

The sides had not been talking directly. Management spokesman Jim Miller described it as "talking on a limited basis," with Martha "passing along messages to both sides." Martha, a former NFL player, is a vice president and general counsel of the NHL's Pittsburgh Penguins.

Martha reportedly was contacted by Garvey after the union chief learned the NLRB had decided not to approve the request by its general counsel to seek the injunction in federal court.

If an injunction had been sought and obtained, the NFL would have been forced quickly to present an improved wage scale proposal. Now, the NFL and the union will appear before an administrative law judge here Nov. 29 to argue the NFLPA's claim that the league has refused to bargain fairly.

General counsel William Lubbers had asked the full NLRB to grant him authorization to seek a preliminary injunction in U.S. District Court. The board refused to give reasons for denying Lubbers' request, but apparently felt the league's alleged violations did not warrant such drastic action.

That decision was a major blow to the union, which had been pressing hard for an injunction after the issuance in Lubbers' name of a complaint against the league.

In the negotiations, both management and union sources said earlier they were at an extremely delicate stage and could move within hours either way: towards a settlement of the strike or to another breakdown in bargaining.

Resumption of the discussions through Martha followed by a week the collapse of the talks for the second time, after eight days of futile attempts to reach a settlement in New York under the auspices of mediator Sam Kagel. Kagel presided over 12 equally futile attempts to mediate a settlement in October in Cockeysville, Md.

It appeared that these contacts between management and the union would likely be the last chance to salvage what remains of the season, after eight games were called off because of the strike. The regular season has 16 games; two were played before the strike was called Sept. 20.

The focus of Martha's efforts as an intermediary were said to be concerns and objections raised after management made details of its 75-page offer, presented to the union Nov. 6, available to its 28 clubs and told them to share that material with individual players.

Since then a number of players have told the union to accept the offer, provided certain details can be worked out and ambiguities cleared up; those issues were reported to be what management was addressing in its reworking of the language in some sections of the offer.

Management has insisted since Nov. 6 that it was firm on the money provisions and other major concepts in that offer, but it has said it would be willing to clarify ambiguities and other details for the union.

Among the issues reportedly being worked on tonight were the union's demands that players become eligible for severance pay before they have finished four years in the league. If they are not eligible for severance until they have been in the league four years, the NFLPA contends, that is only an economic incentive for owners to cut them from team rosters just before they have reached their fourth year.