Roger Headrick, 54, a former executive at Pillsbury Co. and Exxon Corp., was elected president and chief executive officer of the Minnesota Vikings, effective Jan. 1, by the team's board of directors yesterday. He'll succeed Mike Lynn, also general manager, who announced two weeks ago that he will leave that post to become president of the NFL's new international spring league.

Lynn said he will remain the executive vice president of the Vikings and will continue to have a vote in team matters. He also said he will continue his general manager duties until Jan. 1.

Headrick is a member of the 10-person partnership group Lynn put together in 1989, although that partnership is involved in litigation. Lynn controls two-thirds of the team's voting stock through the partnership, which has yet to be approved by the league.

The Vikings' corporate structure has been in court for about five years, since former team president Max Winter sold his one-third voting stock to banker Carl Pohlad and businessman Irwin Jacobs. Pohlad, who owns the Minnesota Twins, and Jacobs are suing Lynn's group in an attempt to gain control.

NFL Commissioner Paul Tag- liabue said last week that he would evaluate and resolve significant aspects of the dispute. A Losing Trend

The byword for the NFL used to be parity, but almost midway through the season the word has to be parody: Sixteen of the 28 NFL teams are under .500.

In the last three weeks, just two of the 36 games have matched teams with winning records -- both games between the Giants and the Redskins.

The 49ers and Giants are 7-0, and the Bears, Dolphins, Bills and Raiders are 6-1. The Bengals are 5-3, the Redskins and Chiefs 4-3. That's it for winning records, Pittsburgh, Tampa Bay and Houston being even at 4-4.Sherrard Injured Again

Mike Sherrard, San Francisco's tough-luck wide receiver, will have surgery this morning to insert a steel plate in his broken right leg. Sherrard, a second-year free agent who broke bones in his right leg in 1987 and 1988 while with Dallas, will be out for the rest of the regular season but could be back for the playoffs. He broke his right fibula when he was tackled after a 35-yard catch that set up the winning field goal in a 20-17 victory over Cleveland. . . .

Bengals running back Harold Green was hospitalized after fainting on the team's flight back from a 38-17 loss in Atlanta in which he carried four times for 24 yards. Tests determined Green's blood sugar level is abnormal, said Coach Sam Wyche. Green was released from the hospital in the afternoon. Musical Quarterbacks

For the fifth straight season, a starting Indianapolis quarterback faces surgery that will keep him out for the rest of the year. The Colts have two others still mending and a fourth, the oldest player in the NFL, hasn't played regularly in six years.

"It definitely wasn't a good day to be a quarterback in Indianapolis," said 40-year-old Joe Ferguson after the 27-7 loss to Miami. Signed by the Colts Oct. 17, he completed two of eight passes for 21 yards and was intercepted twice.

Jack Trudeau, who first won the starting job in 1986 when Gary Hogeboom was injured, damaged the anterior cruciate and medial collateral ligaments in his right knee. He's out for the season. Rookie Jeff George, the first player taken in this year's draft, missed three games with a pulled abdominal muscle, then his left knee was bruised in a relief appearance Sunday. Mark Herrmann, in his ninth season, is on injured reserve (separated shoulder) and is not expected back for a week or two.

Ron Meyer has had 15 quarterbacks on the roster for at least one game since he became coach late in the 1986 season. Twenty quarterbacks have been on the roster since the team moved from Baltimore in 1984.