The National Football League and the striking NFL Players Association reached sharp disagreement today over the method of computing minimum wages as negotiators prepared to address the key economic issues of the 42-day-old strike. Management called it a "snag," a union member termed it "going backwards."

Despite what mediator Sam Kagel earlier described as "a real effort to reach agreement" on the part of both sides, it was clear that settlement of the strike was far from certain. Kagel had ordered talks resumed shortly after noon today after a recess early this morning following an exchange of proposals and counterproposals. They were broken off this afternoon, were resumed at midevening, were recessed again before 11 and are supposed to pick up once more Tuesday morning.

Before the resumption, Kagel met for an hour with the player representatives, who reportedly vented their anger.

Ed Garvey, NFLPA executive director, said, "Today was not a very good day."

What the union called a major obstacle arose when management informed the NFLPA that all signing bonuses and incentive bonuses would be included in computing minimum-salary standards. The union said it had assumed all bonuses would be added to minimum salaries.

"I think it stinks. I thought we were here to negotiate a contract," said Don Hasselbeck, the player representative for the New England Patriots. "It looks like we're going backwards."

Jim Miller, a spokesman for the league's negotiators, called it "a small snag typical of labor negotiations. Management maintained that the union should have known all along that the bonuses would be counted in computing minimums."

Some of the player representatives were reported to have been so angry that they wanted to walk out of the negotiations and tell teammates that the season was over. Other union members talked them out of that.

Meanwhile, a spokesman for the NFL Management Council, the league's labor negotiating arm, said even if the dispute is resolved within the next day or two it is unlikely players could be back practicing in time to prepare for games this weekend.

Jim Heffernan, the NFL's director of public relations, declined to speculate, saying only that no announcement would be forthcoming today concerning this weekend's games. But union sources said some player representatives here have been told by their coaches that an 11-game season is better for competitive purposes than a 12-game season; if this weekend's games are called off, the NFL contends that scheduling constraints would mandate a maximum of 11 regular-season games, provided play is resumed by Nov. 15.

Even before the flareup over the inclusion or noninclusion of bonus pay in computing minimum salaries, the sides were sharply divided on that issue. Sunday, management handed the union a minimum salary schedule that would start at $30,000 a year for rookies and increase $10,000 for every year a player is in the league, up to 20 years. The union first had sought a $90,000 minimum for rookies, later reduced it to $81,000 and now has gone back to $60,000.

In his news briefing this afternoon, Kagel said that issues on which the sides are reasonably close to agreement have been assigned to subcommittees while in-depth discussions continue on the major issues.

But, he warned, " . . . in this proceeding it should be clear that the mediator is not a magician. It is the parties themselves that will have to reach the necessary agreement to end the strike."

Kagel's comments to the media were his first since the talks were resumed Saturday.

As the sides returned to the bargaining table this afternoon, management was optimistic that most of the conceptual issues in the dispute had been resolved and that a way could be found to resolve the money issues, which remained substantial.

The union is demanding a $1.1 billion player-compensation package over a three-year contract; management wants a five-year agreement, with $320 million a year assigned to player costs over the last four years of the contract. Money for this season has not yet been addressed because the effects of the strike still are being evaluated.

Management also was reported firm on its insistence for a five-year contract. Union officials say they want only three years just in case the NFL's arrangement with the television networks permits new agreements with cable networks. If it does, the union wants to be able to negotiate for a share of that money.

For the first time since the strike began, the optimism level at Redskin Park rose appreciably after indications of bargaining movement.

"It would be a mistake to get too carried away," said Coach Joe Gibbs, "but I found myself at the blackboard, working on plays with the idea that we would play Sunday. Then I said, 'Wait a minute, what are you doing?'

"We just want to be ready in case something does happen. We already finished a rough game plan for Cincinnati (the scheduled opponent Sunday), but now we are going back and putting in more detail."

Gibbs said he could prepare the Redskins, if necessary, for a game Sunday even if they didn't report until Wednesday.

"Our normal work week is Wednesday through Saturday," he said, "so we would just pick up as usual. But the problem would be reviewing everything, plus working on this specific game. The game plan would tend to be a bit simpler, we'd shorten things up. Only Cincinnati does a lot of things, and they would be hard to prepare for in a short time.

"Everyone knows the negotiations are on a time schedule. It's come to a point where something has to happen this week. If it doesn't, then the talks could go the other way. I'm really waiting to see how things stand Tuesday. They've been canceling the weekend games on Tuesdays."