One year ago yesterday a 3-month-old girl was kidnaped at the old Trailways bus terminal in downtown Washington, prompting one of the largest and longest manhunts in the city's history. Today, while the chance for the baby's return has decreased, the hope, it seems, has not.

The abduction of April Nicole Williams remains the District's only unsolved kidnaping case in memory, and police continue to sift through old leads and look for the unturned stone, hoping that a clue exists somewhere in the stacks of paper work and miles of computer tape.

"We're still reviewing the file to see if there's anything we missed, reevaluating all the leads," said Sgt. Peter Mulligan, the only investigator still assigned to the case from a special task force that once numbered eight police officers.

To mark the one-year anniversary of the kidnaping and to call attention to the plight of missing children, a small rally was held yesterday near the now-closed bus station.

Two of those in attendance were Gary Courm, 32, an electronics engineer in the District, and his 4-year-old daughter, Pia.

"It's important to remember that this can happen to any child," said Courm, holding tightly his daughter's mittened hand. "It's just horrible that someone can be kidnaped and never be found. You just can't imagine that someone would steal a child."

Immediately after April's kidnaping, Mulligan said, "We had a couple hundred calls over a couple of weeks" from people who thought that they recognized the baby or her abductor from pictures and composite drawings that were publicized. Now the telephone calls have all but dried up.

"We've had two or three calls since September," Mulligan said, but he still checks out every one.

And he stays in frequent contact with the baby's mother, Eleanor Marie Williams, now 19, who lost her child when a stranger cradling the infant in her arms walked away, allegedly to get a soft drink, and never returned. Williams, who lives with her father on a farm in Suffolk, Va., recently had another baby.

"We never had much to begin with," Mulligan said. "There was no crime scene where you could get finger prints or precise eye witnesses, and early in the investigation the details were sketchy and not concise . . . . We lost time."

Police staked out the bus terminal at 1200 I St. NW for the next three days, hoping they would find a witness who could provide more details about the abductor. The mother described the abductor as a slender black woman, 5-foot-3, 23 to 25 years old, with short reddish, braided hair.

About a week after the abduction, police returned to the scene with Williams and acted out the kidnaping scenario. Williams then was put under hypnosis, police said, because she was distraught and they needed to clarify the details.

Williams and her child had arrived at the terminal about 3:15 p.m. and were sitting in the main lobby during a three-hour layover between buses when a stanger started a conversation, police say.

During the conversation, according to Mulligan, Williams told the stranger that at one time she had planned to name her baby Latoya Renee.

"That's my middle name," Williams, while under hypnosis, recalled the stranger saying.

When asked April's age, Williams told the stranger that her baby had been born on Aug. 17. The stranger immediately responded: "Oh, I'm a Leo, too."

The stranger then took April in her arms and said that she was going to get a soft drink. That was the last time Williams saw them.

Mulligan says he believes that the stranger may have left the Washington area after the kidnaping, and now can return without having to answer difficult questions about why she suddenly has a baby.

Although it is possible that April, now 15 months old, will bear only a slight resemblance to what she looked like a year ago, he hopes that the child can be identified from a birthmark on her right wrist.

"There will probably come a point somewhere down the line where we'll just have to face the reality that there's nothing more we can do," Mulligan said. "But the book on this case won't be closed until I'm absolutely positive that nothing else can be done."