The case against Tyrone Frazier, the mail carrier accused of allowing his Postal Service jeep to be used in the assasination of a prominent Iranian exile in Bethesda last July was dealt a possibly fatal blow yesterday when a judge threw out statements Frazier made to police.

Montgomery County State's Attorney Andrew Sonner said he would have to study whether to continue the prosecution, but acknowledged that, "I'm not going to deny that [Frazier's] confession in this case was an important part of the evidence."

Prosecution sources said the county expects to drop its case against Frazier but that authorities in the District of Columbia and the Justice Department will be consulted about the possibility of bringing federal charges against Frazier.

Frazier, 31, is one of two suspects in custody in the assassination of Ali Akbar Tabatabai at Tabatabai's Bethesda home last July 22.The man suspected of firing the fatal shots, Daoud Salahudin, also known as David Belfield, is believed to have fled the country the night of the slaying and traveled to Iran.

The second suspect in custody is Horace Anthony Butler, a carpenter, accused of driving Frazier away from a rendezvous with Salahudin at which the letter carrier allegedly lent Salahudin his official jeep. Tabatabai's assassin was dressed as a letter carrier.

In his ruling yesterday, Montgomery Circuit Court Judge John F. McAuliffe found that Frazier's statement that he lent his mail truck to the man accused of shooting Tabatabai came after FBI agent improperly induced the mailman to change his story that he had been kidnaped by promising him special treatment.

Sonner said the FBI agents, used to working under federal laws, "apparently stumbled on a Maryland interpretation" of state laws that he said are more stingent than federal statutes forbidding police from inducing statements.