The 28 National Football League coaches know they are in a high-risk profession often governed by the tyranny of chance, the funny bounce of a ball for instance. And occasionally by the incompetence of game officials on an important play.

The coaches were told yesterday by Art NcNally, supervisor of official, what the league has been doing and will be doing to try to prevent, or at least reduce, the major officiating controversies of the 1977 season.

Eight of last year's officials will not return because they are retiring or because they were not invited back although none of those leaving were involved in last season's controversial fumble calls.

Sixteen new officials have been hired, all recruited from the college ranks. Eight will replace those who wil not be back; the others were hired bacause the NFL voted at its recent meeting in Palms Spirngs Calif., to add a seventh official for all games.

At that meeting it also was recommended that two clinics be added for officials during the regular season, in addition to the usual two during the exhibition season.

McNally also told the coaches, meeting for the first time in three years, how game officials are graded on all of the plays in a season - 31,000 in 1977.

Officials are graded weekly by McNally's staff and by coaches in reports to the supervisor, he said. On a scale of one to seven, a grade of four is "satisfactory," seven is outstanding and one is "totally unacceptable."

In the past, crews or set teams of officials were not assembled until the last exhibition game.That process is being moved up two weeks, McNally said.

The official's manual has been revised because of the addition of a seventh official and, for the first time, copies were distributed to the coaches. Previously, the manuals were given only to the supervisor's staff and team officials.

In another matter, the coaches agreed to recommend a change in the recently liberalized pass-blocking rule after realizing that, on draw plays, the play first involves pass blocking, then run blocking.

The coaches will recommend that a new version of the rule be accepted by the club owners when they meet in June.