An Alexandria police lieutenant filed suit yesterday against a detective and a former police investigator, saying they led a conspiracy to discredit him and other city officials by spreading "falsehoods and deliberate lies" about the handling of a drug probe in early 1984.

In a suit filed in Alexandria Circuit Court, Lt. John R. Stedman, head of the Alexandria Police Department's personnel office, charged that police investigator Joseph Morrash and former investigator Charles Cox conspired with City Council member Donald C. Casey, Alexandria Port Packet reporter Alicia Mundy and police officer Morton Ford to make false accusations.

The suit, which asks $550,000 in damages from Morrash and Cox, alleges that the five "secretly worked" to discredit Stedman, Director of Public Safety Charles T. Strobel, Alexandria Sheriff Michael E. Norris, "and indirectly," City Manager Douglas Harman.

"I feel it's an attempt to focus the direction of this probe away from what is at hand and . . . on people who brought the allegations," Morrash said yesterday. "If they think that this will divert our attention, they're dead wrong."

The suit is the latest development in a controversy that has gripped Alexandria since Dec. 20, when an article written by Mundy in the Port Packet newspaper, reported allegations that Strobel had quashed a police drug investigation after Norris's name surfaced on an informant's tape, recorded at Marco's Cafe.

Alexandria Circuit Court Judge Donald H. Kent appointed a special grand jury Monday to investigate the allegations surrounding city officials' handling of the drug investigation.

Stedman declined to comment on the suit yesterday. His lawyer, Phillip J. Hirschkop, said he did not believe it would interfere with the special grand jury's inquiry, expected to be completed in three weeks.

Casey, who pushed for an investigation into the drug probe, is listed as an "unsued co-conspirator" in the suit. He denied the allegations and said he didn't remember ever mentioning Stedman's name in public.

Cox was the principal investigator in the drug probe. He told Morrash and Ford about his dissatisfaction with its handling, and the three jointly alleged that the probe was improperly conducted.

In the suit, Stedman alleges that they accused him of interfering with the drug investigation. However, they say they have never accused Stedman of misconduct relating to the drug investigation.

The Packet reported Dec. 20 that Stedman's name came up in the probe when he dined at the restaurant with Norris, where the two were seen by a police informant working on the case.

Stedman's suit describes Morrash and Cox as "disgruntled" employes who engaged in a conspiracy "to cover up their own ineptness and prior misconduct" and "to punish officials who took actions" against them.

Morrash said the suit may provide a way "to get into the open" other allegations against Strobel and Stedman that Morrash would like to see the grand jury review. When Morrash undertook an internal investigation of those allegations in 1983 at the request of the Alexandria Police Association, Strobel transferred him to patrol.

In October, he was reinstated after an arbitration panel found he had been transferred as punishment for his investigation.

"I think it's the beginning of a series" of court cases, said Norris, who added that though he is not doing anything yet, he and Strobel have retained the services of District lawyer Barry R. Poretz. Strobel yesterday declined comment on Stedman's suit.