Two days before baseball's All-Star Game, National Football League training camps open Sunday with rookies and selected veterans from the Dallas Cowboys, Tampa Bay Buccaneers and Cincinnati Bengals due to report.

The Miami Dolphins and Phoenix Cardinals open camp Monday, and 16 of the 28 teams will be working out by the end of the week. The exhibition season is three weeks away, opening with the Hall of Fame Game in Canton, Ohio, July 30 between Cincinnati and the Los Angeles Rams. The last team to greet its veterans will be Cleveland. The Browns must report by July 28.Miami and San Francisco will meet in the American Bowl '88 in London July 31, every team will play its first game by Aug. 7. The NFL's 69th regular season begins Sept. 4.

The Houston Oilers, New Orleans Saints, New York Giants and Phoenix Cardinals will move their training headquarters this year. The Oilers will train at Southwest Texas State in San Marcos, Texas, after 10 years at Angelo State. The Saints will move to the Unviersity of Wisconsin-LaCrosse after two years at Southeast Louisiana State in Hammond, La. The Giants have moved from Pace University in Pleasantville, N.Y., where they spent 13 summers, to Fairleigh Dickinson University in Madison, N.J. The Cardinals, who moved from St. Louis this year, will train at Northern Arizona University at Flagstaff, Ariz.

The Los Angeles Raiders and Green Bay Packers will open camp under new coaches. Mike Shanahan replaces Tom Flores with the Raiders and Lindy Infante succeeds Forrest Gregg in Green Bay.

Training camps open under the lingering clouds of last year's labor wars. The issue of free agency, which caused a 24-day players strike in 1987, is far from settled.

U.S. District Judge David Doty will decide on the NFL Players Association's request for unrestricted free agency for about one-fifth of the league's players Monday in Minneapolis. The motion stems from the antitrust suit the NFLPA filed against the league last Oct. 15.

If Doty grants the injunction, any player whose contract expired after the 1987 season would be allowed to sign a contract with any of the league's 28 teams, without his original team receiving compensation or the right of first refusal.

Such stars as Philadelphia quarterback Randall Cunningham, linebacker Carl Banks and tight end Mark Bavaro of the Giants, Miami wide receiver Mark Duper and Chicago wide receiver Willie Gault would be made free agents if the injunction is granted.

However, even if the judge rules in the players' favor, NFL management can appeal and delay the freedom sought by the players.

Other important dates in the NFL:

Aug. 23 - rosters must be cut to 60 players.

Aug. 29 - rosters cut to 47. Teams can dress 45 for regular season games, with two players on inactive list.

Dec. 19 - Regular season ends.

Dec. 24 - AFC wild card playoff.

Dec. 26 - NFC wild card playoff.

Dec. 31-Jan. 1 - Divisional playoffs.

Jan. 8 - Conference championship games.

Jan. 22 - Super Bowl XXIII at Joe Robbie Stadium in Miami.

Jan. 29 - Pro Bowl in Honolulu.