Herschel Walker, one of the most spectacular running backs in the history of college football, signed a contract with the New Jersey Generals of the new U.S. Football League yesterday, for a package reported to be worth $5 million over three years, after he was declared ineligible for his senior season at the University of Georgia.

"In denying I signed a contract (last Thursday night), I made a mistake," Walker said in a statement issued by Jack Manton, his lawyer. "No one realizes more than I that I am a human being. I wish to apologize to Coach (Vince) Dooley, the University of Georgia and all the people that have been my loyal friends. I ask for your forgiveness and ask God for his forgiveness."

No terms of yesterday's contract were disclosed, but his lawyer said Walker, last season's Heisman Trophy winner, would be the highest paid player in the history of professional football. Reports of money figures higher than $5 million were said to be inaccurate.

Manton said in Athens, Ga., that all the money in the contract is guaranteed and that investments and interest rates will determine its actual value. According to a source, Walker's deal includes $1 million annually as salary and a $1 million signing bonus. Manton said Walker received a year's salary when he signed the contract about 1 p.m. yesterday.

The Generals will pay the entire contract and no pooling of league monies is involved, according to USFL Commissioner Chet Simmons.

According to the National Football League, Manton also offered the running back's services to the NFL team of Walker's choice as late as yesterday morning. The NFL, according to Commissioner Pete Rozelle, declined because of its rule against signing players with college eligiblity remaining.

Walker, 20, from Wrightsville, Ga., was expected to report to the Generals' training camp in Orlando, Fla., late this week or early next week. The inaugural USFL season opens March 6, when the Generals are to play the Express in Los Angeles.

Yesterday's developments also apparently preclude Walker, a world-class sprinter, from trying to qualify for the 1984 Summer Olympics in Los Angeles. But Manton said Walker's eligibility for the Olympics, since he is not a professional in track and field, may be challenged in court.

Many college coaches and athletic directors were outraged and dismayed by Walker's signing, claiming it could lead to the raiding of undergraduate players by professional teams.

Walker would have had one more year of eligibility left at Georgia. He was the second-leading runner in NCAA history behind former Pittsburgh tailback Tony Dorsett. Walker ran for 5,259 yards, leading the Bulldogs to the national title in 1981.

His move to the USFL ranks historically with quarterback Joe Namath's signing with the New York Jets of the old American Football League when he completed his eligibility at Alabama. Namath's signing went a long way toward assuring the AFL's success and eventually forcing a merger with the NFL.

"It puts the ultimate cap of credibility on the league," said Berl Bernhard, owner of the USFL's Washington Federals.

"He's probably the most exciting college football player of the decade," Simmons said at a press conference in Orlando. "If there were another 11 of him, one for each team, I'd love it."

The Associated Press reported that Simmons promised that Walker's signing was not a precursor to a wholesale raid on collegians "because it was a special circumstance." Simmons said both the league and the Generals believed Walker to be ineligible even before last Thursday because he had hired an agent who came to the USFL team for the purpose of negotiating a contract.

Simmons also said he gave the Generals permission to sign Walker because he had received two outside legal opinions and one from Manton indicating that the rule concerning undergraduates would not stand up if challenged in the courts.

According to Dave Berst, director of enforcement for the NCAA, Walker actually lost his eligibility three weeks ago, when Manton approached the USFL head office to begin negotiations.

Last Thursday night, according to Simmons, Walker met with Generals owner J. Walter Duncan, an Oklahoma City oilman, signed a contract, then rescinded his decision within the grace period allowed. In the days that followed, Walker denied he had signed a contract or jeopardized his eligibility, despite a report Saturday in the Boston Globe that he had.

Simmons said yesterday Steve Ehrhart, USFL legal counsel and director of administration, went to Athens Monday to convey what the league knew to Dooley, Georgia's coach and athletic director. Told Dooley was in Colorado at a speaking engagement, Ehrhart spoke to Mike Cavan, the offensive backfield coach, who relayed the information to Dooley.

Dooley reportedly thought over the information most of Tuesday before talking to Walker that night. According to the NCAA and a statement released by the university, the school did not receive the new information until Tuesday afternoon. The university said two points would make Walker technically ineligible: the negotiation of an agreement and the involvement of Manton.

Under NCAA rules, an athlete retains his eligibility if he seeks only to determine his value as a pro, but loses it if he begins negotiating or has an agent.

Berst said Dooley contacted the NCAA yesterday morning. "We knew what course of action was needed," Berst said. Dooley first contacted the NCAA following the Globe's report of the signing and had invited the NCAA to investigate and satisfy itself whether Walker was eligible or ineligible. That investigation is now moot, Berst said.

The largest annual salary in pro football history, reportedly $806,668, was paid to O.J. Simpson in his final year of playing. Chicago Bears running back Walter Payton is presently the highest paid player. He reportedly made $700,000 last season.

A few hours after Walker's signing was announced, the NFL issued the following statement:

"We were approached by Herschel Walker's attorney and asked if we were interested in signing Herschel and placing him in a franchise city of his choice. For over 50 years the NFL has had rules pertaining to eligibility and the draft that we believe to be in the best interests of the colleges, players and professional football. We have no intention of waiving them for Herschel Walker."

But Manton said that when he talked to NFL Executive Director Don Weiss, "The NFL would have accepted Herschel's name, on a supplemental basis."

Weiss was unavailable for comment but Rozelle, in a telephone interview, said Manton had offered the supplemental draft idea and that it had been rejected. Rozelle also said Manton had called twice, Tuesday about midnight and again yesterday, and told the league he needed an answer by 11 a.m. if it was interested.

That is the time at which Georgia issued its statement. Walker signed his new contract with the Generals about two hours later.

The Generals were at least the second USFL team to offer Walker a contract, but the first given permission by the league office to do so. According to Manton, the Chicago Blitz, operated by former Redskins coach George Allen, mailed Walker an unsolicited contract.

After the Sugar Bowl game Jan. 1, Manton approached the USFL office about the possibility of Walker playing in the New York area. At that time, and at a subsequent meeting, Simmons said, the eligibility rule was explained to Manton and to Walker. "You have to think there was some confusion, but we felt we made the whole question of eligibility clear," Simmons said. "I think he understood the eligibility question."

Walker then requested the meeting with Duncan in Athens. Manton was not present when Walker signed Thursday night's contract. Manton said Walker, a criminology major who intends to attend law school, thought the "right of recision," which he exercised, cleared him of all eligibility problems.

"That's the first thing they teach you in law school," said Dick Dull, a lawyer and the athletic director at the University of Maryland. "He who legally represents himself has a fool for a client." CAPTION: Picture, HERSCHEL WALKER . . . 3 years for $5 million