Quarterback Joe Theismann agreed to a new $1.5 million, four-year contract with the Washington Redskins yesterday that will make him the highest-paid player in the team's history by the time he enters the final year of his contract, it was learned.

The agreement came following a two-hour meeting between the two sides at the Upperville, Va., estate of team owner Jack Kent Cooke, who was negotiating with Theismann for the first time since the talks began last June.

Both Theismann, 32, and Cooke confirmed that they had come to terms for what the veteran quarterback said "was more money than I anticipated they'd offer me and more than I had geared myself to accept."

Cooke said he gave Theismann, a free agent after the 1981 season ended, "more money than he had been asking for."

Although neither side would reveal details of the contract, team sources say that Theismann will earn $300,000 this season with yearly increases until he reaches $415,000 in 1985.

John Riggins signed a contract in 1976 that has paid him $300,000 annually. Riggins did not play in 1980 and was not paid, but rejoined the team in 1981. This year, the Redskins will either sign Riggins to a new contract or pay him his option-year salary of $330,000, which would be the highest in team history for now.

Theismann, who was paid $225,000 last year and was not among the top 10-paid quarterbacks in the NFL, moved closer to that range yesterday. Archie Manning of the New Orleans Saints is believed to be the highest-paid quarterback, earning $600,000 a year. Ken Stabler of Houston is paid $470,000, followed by Pittsburgh's Terry Bradshaw ($450,000) and Cleveland's Brian Sipe ($410,000).

"I am very satisfied with what transpired today," said Cooke, who agreed to the meeting after it had been requested by Ed Keating, Theismann's agent.

"Being able to meet face to face with Mr. Cooke was the key," said Theismann. "We are the two people who are personally involved here. It adds a little bit of personal touch to it, and that's the kind of thing I respond to. What he offered pleasantly surprised me."

Until yesterday, Theismann's only surprises in the negotiations were mostly negative. He was stunned over the Redskins' hard-line tactics and had directed Keating to talk to other teams. But all seven clubs Keating contacted either turned down Theismann or didn't respond to the inquiries. Under terms of the current NFL contract, it would have cost a team two No. 1 draft picks as compensation to the Redskins to sign Theismann.

It was inferred from the Redskins' negotiating approach that they were not completely satisfied with Theismann, despite their public statements that they wanted him to sign a new contract.

In turn, Theismann, who originally asked for $1.8 million, admitted he was disillusioned by what was happening and puzzled over why the Redskins would treat him in such a cold fashion. Theismann sought a new contract before the start of the 1981 seson, but was unable to come to terms with General Manager Bobby Beathard. This upset Theismann at times during the course of the past season. But yesterday he said that was all history.

"I'm very happy, it all worked out and that's what is important," said Theismann, who has numerous business ventures in the Washington area and is a popular figure here. "With something this important, I knew it was going to take time to solve, so I made up my mind that once it's resolved, it's resolved.

"I said I always wanted to continue to be a Redskin and now that has come true."

The initial breakthrough in the negotiations came last month when Theismann and Keating, anxious to end the discussions, came in with a new proposal that lowered their original offer by $200,000. It was coupled with a request to meet directly with Cooke instead of negotiating only with Beathard.

Theismann, who will be 33 in September, has played seven years with the Redskins after three years in the Canadian Football League. Last season, his first under Coach Joe Gibbs, he passed for 3,568 yards, a career high, and turned in the second-best season overall statistics of any quarterback in Redskin history. He completed 293 of 496 passes (59.1 percent) for 19 touchdowns and also scored twice rushing.