The New Jersey Nets disciplined Micheal Ray Richardson yesterday for missing Monday's practice and sent him for a drug test on which the fate of his often brilliant but cocaine-plagued pro basketball career will ride.

Lewis Schaffel, Nets executive vice president, said Richardson, who claimed to have a case of flu Monday, was to undergo the drug screening at University Hospital in Newark. Nets officials said they expected the results to be announced by the NBA today.

"The truth is not in his word," Schaffel said. "It's in the test."

The team also fined its star guard an undisclosed amount for missing the practice and a doctor's appointment Monday, only three weeks after he had been reinstated following 15 days in a California drug rehabilitation center.

If the test turned up the presence of drugs, it would be a third offense for Richardson, 30, meaning he would be banned from the league for life, although with the option of appealing after two years.

Richardson, the 1984-85 NBA comeback player of the year, leads the Nets in scoring with a 16.3 average and assists with 7.5 in the 40 games he has played this season. He also had drug problems before the NBA instituted its three-times- and-out policy.

Richardson, who signed a four-year, $3 million contract before the season, would not comment on how much he was fined. He admitted he made an error in not phoning team officials after failing to keep an appointment with Dennis Quinlan, the team physician, who had been testing Richardson's urine weekly.

Richardson arrived on time for the Nets' shoot-around at 10 a.m. yesterday, but did not take the court. Until the suspension, Coach Dave Wohl had projected last night's game against Detroit as Richardson's first starting assignment since rejoining the team Jan. 22.