U.S. District Judge Harold H. Greene yesterday dismissed drug charges against a Takoma Park woman, saying federal prosecutors improperly pressed her into cooperating in a drug investigation.

That was an abuse of the grand jury process and "the product of inappropriate conduct," Greene said. He did not single out individual prosecutors for their handling of the case, but limited his remarks to a general criticism of the way the mother was handled by the U.S. attorney's office here.

The ruling came in a case involving Esther D. Fields, 35, who was operating an unlicensed nursing home at 4500 14th St. NW when she was indicted.

She was charged with illegally selling the painkiller Dilaudid to drug addicts who used it with heroin. She obtained the drug illegally from Dr. Samuel Rosser by telling him she was having trouble obtaining medicine for terminally ill patients at her nursing home, according to investigators.

She was indicted in June 1978, apparently on the basis of Rosser's testimony against her. Greene said yesterday that Rosser himself was the target of the investigation and should not have been believed by prosecutors.

However, last August the government dismissed the charges and said it could no longer vouch for Rosser's credibility.

Rosser then pleaded guilty in the investigation in April of this year, and the government renewed its probe of Fields and reindicted her again this May.

The government claimed that it always intended to prosecute Fields for her role in the drug scheme, but Greene said yesterday he did not believe the government had any motives but to try to pressure Fields to cooperate and then punish her when she failed to do so.

Greene agreed that the government sometimes use pressure to force a reluctant witness to cooperate, but said it went too far when it asked a grand jury to indict her.

Technically, the 23-member grand jury is independent of any prosecutor's influence, but it is well known, and as Greene noted, "a melancholy fact," that grand juries have become "mere instruments of the prosecution."

He said the government did not have a case against Fields the first time around and that it was wrong to allow the grand jury to induct her without sufficient evidence.

Since the government acted improperly in bringing the first case against Fields, the second case must be dismissed as well, Greene said in barring all future prosecution against her in connection with the drug sales.

Stephen W. Grafman, who represented Fields, said the incident is "the classic case of what I consider to be the abuse of the grand jury system" by prosecutors.