On the verge of pleading guilty in the hit-and-run death of a roller-blading American University freshman, Shane Simeon DeLeon backed away from the plea yesterday in D.C. Superior Court.

Defense attorney Renee Raymond declared that the plea would not go forward and apologized to the student's mother, Kathleen O'Dell, who had traveled from Upstate New York to witness the proceedings in the Jan. 28 death of her son Matthew.

Raymond and the prosecution had asked Judge Patricia A. Wynn to schedule the hearing to receive a guilty plea from DeLeon. Raymond declined to discuss the change of plans, which came one day after a front-page story in The Post revealed that the original chief detective in the case was demoted for poor work.

O'Dell did not have any comment after the announcement in court.

Fourteen traffic fatality investigations assigned to District Detective Milton A. James were reassigned to other detectives. The O'Dell case is one of them. The police work was so slipshod that no arrests are likely in two of the cases, law enforcement sources said.

James did not question several important witnesses in the O'Dell case and did not gather other evidence that could have placed DeLeon behind the wheel, sources said in April. The case against DeLeon gathered strength, however, after Detective Joseph R. Diliberto took charge of the inquiry.

Witnesses said DeLeon, who lost his Maryland driver's license in 1994 after two drunken-driving convictions within a six-month period, drank four large draft beers at a Wisconsin Avenue pool hall on Jan. 28.

Using his current District license, he then drove his white 1998 Ford Ranger to the house where he was staying on MacArthur Boulevard, investigators believe.

On Nebraska Avenue NW, DeLeon allegedly slammed into O'Dell, 18, who was roller-blading with a friend. The Ranger did not stop.

Later, DeLeon reportedly told a witness that he thought he had hit a trash bag.

Police located the Ranger. Its windshield and right-front grill had been damaged. Hair taken from the windshield contained O'Dell's DNA, according to an FBI study performed for District investigators. DeLeon refused to answer police questions about the night of Jan. 28, sources said.

Prosecutors charged DeLeon with second-degree murder. No trial date has been set.

CAPTION: Shane Simeon DeLeon, right, stands with defense attorney Renee Raymond at his arraignment in April.