Charles Wantland, the ex-convict accused of murdering a 12-year-old Clinton boy last summer, told police he blacked out on the day of the slaying after taking the boy home with him to see a model boat, prosecutors said yesterday.

As Wantland's trial opened in Prince George's County Circuit Court, prosecutors focused on three oral statements the defendant allegedly made to police and said they will prove Wantland sexually molested and fatally stabbed Donald Alan Henley on June 17, 1978, in the woods near his home.

Defense attorneys contended that the statements on which the prosecution's case centers were taken in violation of Wantland's rights.

The body of Henley, stabbed 14 times, was found by searchers a few hundred yards from the Berger mansion, a deliapidated old county homestead, the day after he had disappeared while running home from an outing with a playmate. Wantland, who had been paroled from a Maryland correctional institution about three weeks earlier, lived and worked at the mansion in a federally funded job training program.

Yesterday, Deputy State's Attorney Joseph Sauerwein told jurors that in one statement to police Wantland said he gotten to know Henley in the weeks before the slaying, had "come to like him very much" and had sexual relations with him three times. According to Sauerwein, Wantland said that on June 17 he met Henley on the street and took him to his room at the nearby Berger mansion.

In the same oral statement, Wantland allegedly told police that the "last thing he remembers was around 4 p.m. standing by the mansion near a pond," according to Sauerwein. Wantland's next recollection was later that night, hearing searchers call out for Henley and knowing "that something was wrong," Sauerwein told jurors.

"He did not know what made him kill the boy, if he did kill him," Sauerwein said Wantland told Prince George's police. "But he knows he gets violent when drunk and unknown things can set him off into a rage."

Sauerwein said Wantland also told this same officer that he had been drinking the night before Henley was killed and was drinking again that morning.

"'I must have done it. I must have done it. I just don't remember'" Sauerwein quoted Wantland as saying when asked by one police officer what had happened the day of the slaying.

When it was the defense's turn before the jurors, attorney Joseph Niland asked them to consider "all the circumstances" that surrounded the taking of the three alleged statements.

Niland said the first was obtained after the 44-year-old Wantland had indicated on an official police form that he did not wish to give a statement without an attorney present. Wantland, however, did not get to see an attorney that night.

Niland said there "will not be a single piece of evidence to corroborate" the statements his client allegedly made to the police officers.

Niland also attacked the identification that will be made by one of the key prosecution witnesses - the only one who allegedly saw Wantland and Henley together on the afternoon the boy was killed.

Niland said that this witness first told police the man he saw with Henley was wearing a turquoise shirt, while all the other prosecution witnesses will testify the man was wearing a light-colored jacket.

Yesterday, several witnesses took the stand and identified Wantland as the man they talked to or noticed in Henley's neighborhood on the afternoon of the slaying.

Jeffrey Delcher, Henley's 11-year-old friend, told the jury how he lost sight of Henley as both boys ran home to get out of rainstorm between 3 and 4 p.m. on the day of the slaying.

"We started to run. We were together. Eventually we became separated," Delcher said. "I looked back and saw him. I looked back again and didn't . . . I couldn't find him, so I went on home."