Michael Ray Richardson, the New Jersey Nets guard who disappeared Friday, admitted yesterday that he is again suffering from a drug problem and turned himself in to National Basketball Association drug counselors for treatment.

Lewis Schaffel, the Nets' executive vice president said Richardson, 30, will be suspended without pay indefinitely while he undergoes treatment, to be paid for by the club under the NBA's drug policy. The length of rehabilitation will be determined by the drug center's staff, the league and the Nets, Schaffel said.

"I feel terrible about this," Schaffel said. "I feel sorry for him. As an organization, we wish him well and will stand by him."

Richardson dropped out of sight Friday night following a team Christmas party. He telephoned his wife Saturday and telephoned his agent, Charles Grantham, after the league decided Monday that Richardson would not be subject to permanent dismissal if his disappearance were drug-related.

Richardson twice before has been through cocaine addiction rehabilitation, the last time in 1983 when he was suspended by the Nets for two months . . .

General Manager Stu Inman of the Portland Trail Blazers will be leaving the team, the Oregonian newspaper reported. The newspaper said the Blazers are planning to announce Thursday that Inman is stepping down "to pursue other opportunities in the National Basketball Association."

Inman, a coach at San Jose State from 1957 through 1966, has been with the Portland NBA franchise since its inception in 1970.