Half of the 28 teams in the National Football League will lose money this season, Jack Donlan, the NFL Management Council executive director, estimated today.

If accurate, Donlan's prediction would represent a marked decline in individual team finances over the last three seasons.

Four teams lost money in 1984 and seven in 1985, Donlan said at a news conference at the NFL winter meetings.

But Donlan said this is not unusual when the league nears the end of a television contract. The NFL's present deal with the networks expires after this season.

Donlan refused to call the league's financial situation a "crisis." "I don't like to be the prophet of gloom and doom," he said.

Salary escalation appears to be the chief culprit. In 1985, player costs (a large majority of which are salaries) averaged $15.3 million per team. Television revenue per team averaged $16.2 million, which means there was an average net between the two figures of $900,000 per team.

But, Donlan said, in 1986, player costs and television revenue are expected to be the same -- an average of $17.5 million per team.

"It's a wash," Donlan said.

Donlan said player salaries increased 20 percent last year to an average of $202,000. He expects the average salary this season to be $235,000. In 1981, the average salary was $90,000, he said.

In other developments today, the league approved a preseason game between the Chicago Bears and Dallas Cowboys in London's Wembley Stadium on Aug. 3.

The instant replay, approved Tuesday by a 23-4-1 vote, does not include an appeal procedure for coaches, as the U.S. Football League instant replay did. The NFL's rule stipulates that reviews and changes of calls will be controlled by the officials on the field and in the press box.

The NFL confirmed that it had turned down an offer to settle its suit with the U.S. Football League by accepting four USFL teams in a merger.

The USFL, however, promptly denied it had proposed any settlement.

NFL spokesman Joe Browne said the offer had been made at a meeting in New York last week between two lawyers -- Robert Fiske for the NFL and Harvey Meyerson for the USFL -- after Peter Leisure, the presiding judge in the case, suggested the two sides look for a way to settle the $1.32 billion antitrust suit.

Browne said the league had flatly rejected the offer, which would have brought the Memphis Showboats, Baltimore Stars, New Jersey Generals and an unspecified fourth team into the league.