The D.C. police detectives deliberately lied to a youth three times about the evidence they had collected against him in connection with an assault on a woman who was beaten and robbed of her pocketbook in July, 1977, the D.C. Court of Appeals wrote in an opinion yesterday.

Nevertheless, the appeals court said, the lies and trickery were not enough to invalidate the youth's confession to the crime, and the court upheld his conviction of robbery.

The court noted that the youth, who is just under 18 years old, had been arrested five times and was "somewhat sophisticated" in dealing with law enforcement officials.

The appeals court, in an opinion written by Judge Frank Q. Nebeker, supported a juvenile court judge's finding that the youth was "making an attempt to 'outsmart' the police, who in turn were trying to 'outsmart' him."

According to the opinion, the youth was picked up by police shortly after the robbery in the 3500 block of Rittenhouse Street N.W. Detectives told the youth that they had seen hin in the neighborhood earlier, which they had not informed hin that his fingerprints were found on the woman's pocketbook, which was not true, and then told him the victim had identified him as her assailant, which she had not, the appeals court said.

At that point the youth, who was not identified in the opinion, admitted he committed the robbery and signed a written confession, the appeals court said.

The appeals court said that the youth was repeatedly informed of his constitutional right not to make a statement and had cooperated voluntarily with the police. The court also said that during the course of the questioning by police, the youth had come up with various versions of his whereabouts and activities at the time of the robbery.

Taking all the circumstances into consideration, the appeals court said, the deception by police was not enough to induce a confession. Judge Catherine B. Kelly and former Chief Judge Andrew M. Hood, who is now retired, joined with Nebeker in the decision.