A federal jury in Baltimore deadlocked yesterday in the case of a Navy physicist accused of using the Internet to try to seduce a teen-age girl, although most of the jurors rejected the defendant's claim that he was only engaged in an online sexual fantasy.

Jurors hearing the case in U.S. District Court against Navy weapons designer George Paul Chambers split 9-3 in favor of conviction.

In interviews, jurors said that the holdouts generally accepted Chambers' argument that he never thought he was dealing with a real child when he exchanged sexually explicit e-mails and made arrangements to meet with an undercover FBI agent posing as a 13-year-old cheerleader.

Jury forewoman Sarah A. Shifflet said she refused to vote for conviction, noting the inherently shadowy nature of Internet communications that make it impossible to really know who is on the other end of the line.

"People do misrepresent themselves, and it's not a gross misrepresentation for him to engage in something like that and not know," Shifflet, 30, of Perry Hall said outside court.

After about 11 hours of deliberations over two days, most of the other jurors said the deliberation process was frustrating because they were convinced that Chambers was guilty.

"The majority felt he thought he was dealing with a 13-year- old; he thought that's who he was going to meet," said juror Keith D. Floyd Sr., 50, of Linthicum.

Chambers, 45, of La Plata faces a second trial on the single-count indictment of using interstate commerce - in this case, the Internet - to try to induce a minor to have sex.

Judge Andre M. Davis asked attorneys in the case to advise him by Dec. 20 on how they plan to proceed.

Prosecutors declined to comment last night.

Chambers' attorney, Bryan A. Levitt of Owings Mills, said he was "in a small measure gratified that there was no conviction."

"Obviously, I would have liked to put an end to it today with an acquittal," Levitt said.

If the case is retried, he said he would put on the same defense: "I don't think there will be a different result."

Asked how he felt about the outcome, Chambers sighed heavily and declined to comment.

He was arrested in June after exchanging graphic photographs and e-mails for months with an undercover FBI agent working to track and thwart online child predators as part of the government's $10 million "Innocent Images" program.

Authorities arrested Chambers at The Mall in Columbia, where he had arranged in a series of online chats to meet the girl. At trial, Chambers testified that he didn't think he really was talking to an underage girl in an America Online chat room called "I Love Older Men" and went to the mall only out of curiosity.

Chambers, who is married with two young daughters, testified that the anonymity of the Internet allows everyone to pretend to be someone they aren't.

"I didn't believe I was doing anything wrong with fantasizing on the Internet," he said. "That is not a crime. You would have to put 10 million people in jail if it were."

The FBI sting that led to Chambers' arrest was nothing new in the world of online policing. But Chambers' decision to take the case to trial was rare.

In federal courts across the country, such cases almost always result in guilty pleas without further appeals.

Investigators can produce word-for-word transcripts of each online conversation, and they typically are so graphic and embarrassing that few defendants are anxious to have them read aloud to a jury.

Federal prosecutors said Chambers believed he was interacting with a real teen-ager in the more than 100 messages he exchanged with undercover FBI Special Agent Emily Vacher between February and June.

They said his correspondence, and the arrangements to meet in Columbia, showed that he in fact wanted to meet the girl and to have sex with her.

"The issue is not whether there are people on America Online who like to fantasize about sex," Assistant U.S. Attorney Jonathan P. Luna said in closing arguments Wednesday.

Government lawyers tried to refute Chambers' claim that he was not interested in young children sexually by showing the jury photos of child pornography found on Chambers' laptop computer.

Court records showed that Chambers warned in one e-mail that he needed to be careful because "sometimes, cops pretend to be teen-agers online."