A three-judge panel of the D.C. Court of Appeals voted yesterday to uphold the constitutionality of a new city law that allows persons charged with first-degree murder to be held without bond pending trial.

But, in an unusual move, the judges asked the full nine-member court to vote on whether it wanted to hear arguments on the issues before the panel issued a formal opinion.

The panel's decision came just hours after the city's Public Defender Service urged the judges to throw out the law -- part of the city's new package of tighter bail laws -- arguing that it could allow murder defendants to be held indefinitely.

Under court rules, if five judges vote to hear a case, it is argued again before the full court. If a majority declines to hear this case, the panel will issue its opinion upholding the law.

PDS lawyer James McComas argued before the panel yesterday that the provision, which went into effect in July, violated constitutional guarantees of due process because it set no limits on how long a murder defendant could be jailed prior to trial.

McComas said the new law allows the government to hold a suspect for nine months before indictment and then "for years" before trial.

Assistant U.S. Attorney Judith Hetherton argued that the law is valid and that court rules and the ability of judges to review each case ensure that no one would be held indefinitely.

In answer to a question from a judge, Hetherton said it was "possible" that a person could remain in prison for as long as two years before trial, but she said there are "safeguards if a judge believes the government has abused the law."

Hetherton also argued that the protections afforded defendants under the city law are greater than those required by the Supreme Court.

The city passed a law in 1970 that said persons accused of crimes punishable by death could be held without bond. In 1972, the Supreme Court declared the District's death penalty statute unconstitutional, but the law allowing detention without bond in capital cases has never been challenged.

Last July, the City Council, as part of an anticrime package aimed at repeat offenders, amended the 1970 law to allow prosecutors to ask that anyone accused of first-degree murder be held without bond until trial.

Since that law went into effect on July 9, law enforcement officials estimate that prosecutors have used the provision about 50 times, or in virtually every first degree murder case to come before the court. Judges have granted the request about 80 percent of the time, according to prosecutors.

The appeals yesterday were brought on behalf of three persons being held without bond under the law, including Leslie deVeau of Northwest Washington, who is charged in the March 18 shotgun murder of her 10-year-old daughter.

The judges on the panel, Julia Cooper Mack, Frank Q. Nebeker and William C. Pryor, gave no indication as to when they might rule.