ROSEMONT, ILL., OCT. 12 -- The National Football League players' union offered today to return to work immediately if team owners agree to mediation and binding arbitration of the players' three-week-old strike.

The offer was made at the conclusion of a tense six-hour meeting of player representatives from each of the 28 teams as television ratings for the second weekend of NFL games with mostly replacement players fell again, while the pressure of going without paychecks weighed ever heavier on most of the strikers.

After six weeks of mediation, the unresolved issues would go to arbitration no later than the end of the regular season, according to the union proposal. Under terms of the proposal, all striking players would be reinstated for the remainder of the season; the 1982 collective bargaining agreement would stay in effect until the end of the season or until a new agreement is reached; and union officers, player representatives and their alternates would be protected on rosters for the rest of the season.

Upshaw, who said the players would not return without a written agreement to these conditions, added: "If the owners refuse to accept this, we're out for the duration."

Jack Donlan, the executive director of the Management Council, said late tonight there was no chance for the plan to be accepted.

"We told Gene {Upshaw} many times times we're not interested in arbitration," he said.

Tex Schramm, president of the Dallas Cowboys, said: "We'll study the proposal. But we're not in favor of putting the future of the NFL in the hands of a single arbitrator."

In mediation, a third party attempts to help the two sides resolve issues and keep the negotiations moving. In arbitration, a third party reviews the proposals of each side and decides a final outcome that is binding on each side. The arbitrator can take the extreme position of either side or can decide on a middle ground. Several NFL owners are concerned over the ruling by an arbitrator that gave baseball free agency a decade ago and subsequent decisions in favor of players in salary arbitrations.

Today's action took place less than 24 hours after the entire Washington Redskins regular team met at quarterback Jay Schroeder's home, where the consensus favored a return to work, under certain conditions.

"We had to make a move," center Russ Grimm said tonight. "We're dying a slow death. "The benefits {from a new contract} are not going to make up for our losses."

Of the union proposal, Grimm said, "That's what we wanted {movement from the union}. You can't move much further than that."

There were reports that the Management Council, scheduled to meet in New York Tuesday, was meeting via telephone conference call tonight and might be asked to call a meeting of all 28 owners to decide the issue.

All major issues remain unresolved, including free agency, pension -- which NFLPA president Marvin Powell of the Tampa Bay Buccaneers today called the main issue -- severance, drug testing and length of contract.

The owners offered to send the dispute to mediation before the players went on strike Sept. 22, after two games. But the players rejected the proposal, saying it was acceptable only if the owners agreed to binding arbitration, which management rejected.

Doug Allen, Upshaw's assistant, said: "We're going to have a collective bargaining agreement in one of two ways -- this way, or by the players staying out until this is resolved."

Upshaw said he hoped the regular players could be back in uniform in time for Sunday's games. If not, however, he said he hoped NFL Commissioner Pete Rozelle would cancel the scheduled third weekend of games played by replacement teams.

When asked why the owners would consider the union's proposal, Upshaw said, "they can't be satisfied with the product that's out there. We'll find out how bad they want the players back."

Today's action followed Upshaw making public a letter he sent to ownership of each of the 28 clubs, telling them that if they knew "what was happening and wanted to make a deal, it could be done in a couple of hours."

As the players met in this Chicago suburb, three more players joined about 130 of the 1,585 NFLPA members who had crossed the picket lines to join replacement players, and the overnight figures of the nation's 15 largest markets showed that television ratings dropped for the second straight week, this time by about 10 percent.

Management also declined to say what it would do with the replacement players if the regulars players return this week. Some owners were said to believe that if the regular players returned, they would walk out again Saturday in an effort to put this weekend's games in jeopardy.

Sources said a league rule allows, in case of a strike, if more than 15 players return to a team, the clubs may have unrestricted active rosters. Some management sources hinted that teams initially would keep both regular and replacement players and practice the replacements at a different time or site.

In his letter, Upshaw bypassed Jack Donlan, the owners' chief negotiator, whom he blamed for the stalemate.

"To put things in simple terms, it appears either that the owners are trying to bust the players or that a majority of the owners don't realize what is really happening at the table," Upshaw wrote.

". . . I know that many of you want to find the middle ground and get the players back to work. I appeal to you to get that accomplished by whatever means you can. The players won't let any single issue be a stumbling block in these negotiations. The only thing that can prevent a settlement is the continued intransigence of your leadership at the table."

John Jones, a spokesman for the Management Council, declined comment on Upshaw's letter. A management source said the league issued a directive late yesterday for owners neither to comment on the letter publicly nor to reply to it.

Ownership is solidly behind the labor negotiations committee, according to sources. "I've not heard an iota of disunity in the NFL," said Cleveland Browns owner Art Modell before the letter was made public.