A federal judge in Alexandria, after hearing that Emmett Muriel Grier III was drawn into crime "out of a sense of desperation and weakness," sentenced the Detroit man to 46 months in prison yesterday for demanding $75,000 from Tammy Brannen in exchange for the return of her missing daughter.

"This is an unfortunate situation," said U.S. District Judge Claude M. Hilton. "It was a particularly egregious offense, yet committed by a young man who's done some very fine things and has some potential."

Grier, 20, a former Howard University student, pleaded guilty April 16 to conspiracy, extortion, making threats of violence, possession of ransom money and illegal use of a telephone. He admitted making two phone calls to Brannen in mid-February and threatening to hurt her 5-year-old daughter, Melissa, if she did not deliver ransom money to a drop site near Union Station.

Neither Grier nor co-conspirator Anthony Girard McCray was ever connected to Melissa's disappearance. The girl, whose sixth birthday was in April, was last seen at a Dec. 3 community Christmas party near her Fairfax County home. Grier and McCray, also convicted in the case, were arrested by FBI agents Feb. 15, shortly after an unknowing courier picked up the ransom money and delivered it to a Howard dormitory.

David H. Hopkins, Grier's attorney, argued yesterday for leniency for his client, noting that Grier pleaded guilty without seeking a deal with the government, voluntarily asked that his bond be revoked and that he be jailed the day he pleaded, and provided crucial testimony at McCray's trial.

Hopkins also noted that Grier sent an apologetic letter to Tammy Brannen, but said he did not know its contents.

Hopkins said the extortion attempt was "an egregious affront on a woman whose suffering was already unimaginable," but that Grier had accepted responsibility and with the help of his family had gained a maturity he had not previously possessed.

Maintaining that Grier, once an honor student, was easily duped by McCray into participating in the scheme, Hopkins read parts of a psychiatric evaluation in which Grier is described as "restless, angry, rebellious."

Grier "masks his true feelings with a show of bravado," Hopkins read. " . . . He appears to feel in great danger much of the time . . . and out of a sense of desperation and weakness he tends to follow along."

Hilton denied Hopkins's request that Emmett M. Grier Jr., the defendant's father and a sheriff's deputy in Detroit, be allowed to address the court on behalf of his son.

Asked by Hilton to summarize the father's sentiments, Hopkins said: "Mr. Grier, if able to testify, would say that this terrible event has brought him and his son closer together" and that both have learned and grown from the incident.

U.S. Attorney Henry E. Hudson, who prosecuted the case, told the court that Grier and McCray "knew that Mrs. Brannen was suffering . . . and would be easy prey."

Hudson condemned Grier for making the extortion calls "that sent chills up that woman's spine." But he conceded that Grier had cooperated fully with the government, accepted responsibility for the crime and fallen prey to criminal acts instigated by others.

McCray, 24, from Canton, Mich., is scheduled to be sentenced Wednesday. He faces a prison term of up to 60 years.