Negotiations between the National Football League and the striking NFL Players Association reverted to form today, as talks between the sides abruptly were recessed for seven hours amidst a sharp disagreement over the applicability of unfair labor practice charges once the strike is over.

But negotiators returned to the bargaining table about 8 p.m. today and met for about 5 hours before recessing until 9 a.m. Saturday. Sources said progress was slow.

The night meeting followed a bizarre day of charges and countercharges despite the imposition of a news blackout.

After a marathon bargaining session that ended shortly before 6 a.m., the talks were resumed five hours later, then broken off after five minutes.

Al Zack, a union spokesman, said the players called a caucus because management had demanded that the union immediately drop all unfair labor practice charges pending against the NFL Management Council, the league's labor negotiating arm.

But Jim Miller, a council spokesman, met with newsmen later in the afternoon and denied Zack's contention. The talks were recessed, he said, because the union wanted to "continue and institute new litigation after an agreement." He said management was awaiting arrival of a list of the litigation the union had in mind before returning to the bargaining table.

Within an hour, the NFLPA issued a press release calling Miller's statement "nonsense."

"We will have no further comment on it," the release said. "Mediator Sam Kagel has emphasized to us that the news blackout is still in effect."

Today's back-and-forth exchange of recriminations was in marked contrast to what union spokesmen had described as two days of progress on noneconomic issues as the NFL's first regular season players' strike entered its 25th day. Negotiators were preparing to tackle economic issues today, the NFLPA said.

But Miller said a substantial amount of work remained to be done in the noneconomic area before economic matters could be addressed.

Both sides agreed that the major stumbling block to a settlement has yet to be dealt with. That is the union's demand that a trust fund be set up to pay players' salaries on a seniority-based scale with performance-incentive bonuses, and management's opposition to that concept.

In any event, neither side was prepared to walk away from the mediation process over today's issue of the unfair labor practice charges.

"We're not going anywhere. We're here to bargain," said Zack, who said management negotiators had insisted that the unfair labor practice charges be dropped as a precondition of continuing the talks. Such an agreement would be an open invitation to management negotiators to "stonewall it" in the talks, he said.

Miller flatly denied that the NFL had made any such demand. "It's not true that the management council preconditioned the continuation of bargaining on anything," he said. "The negotiations have been bruised but not shattered."

Each side has filed several unfair labor practice charges against the other, including failure to bargain in good faith over wages.

According to well-placed sources at the National Labor Relations Board, the general counsel's office was prepared this week to decide whether to issue a complaint concerning the union's charge that the league had bargained in bad faith. But it was decided not to proceed that far while mediation here was in progress.

The other unfair labor practice charges, in various stages of resolution, include contention by the union that the NFL has dropped players because of their union activity, refused to supply information essential to bargaining and refused to comply with terms of the old collective bargaining agreement.

Management has charged that the union has been guilty of unfair labor practices by refusing to meet at reasonable times and places to bargain and of illegally attempting to dictate the composition of management's bargaining committee by insisting that team owners participate in the negotiations. Those charges are being investigated by the NLRB.

The NLRB has ruled in favor of the union on two of its charges and an administrative law judge has ruled in the NFLPA's favor on two others.

The administrative law judge ruled last month the league was wrong in refusing to give the union copies of all player contracts and the noneconomic terms of its television contracts. The union said it needed that information to bargain effectively; the NFL is appealing the ruling to the full NLRB.

Also last month, the union won on its complaint that Sam McCullum, the player representative for the Seattle Seahawks, was fired because of his union activity. And, a complaint has been issued against the NFL for refusing to suspend San Diego Chargers quarterback Dan Fouts last year for refusing to pay his union dues. Both cases await hearings before an administrative law judge.