A delusional Britney Spears is "optimistic" she'll get her kids back today when she tells the court she missed her mandatory drug test because of a scheduling snafu.

"She is feeling very optimistic about the future," Spears' pal Sam Lufti told Us Weekly yesterday, brushing off Spears' drug-test delinquency as a minor mixup.

"There were scheduling conflicts and some errors in communication as to times and places for drug tests . . . but they're all squared away now," he said, as if Spears had missed a weave appointment rather than a stern judge's order.

"She is hoping the judge will reverse the order" giving full custody of her boys to her ex-husband Kevin Federline, Lufti said, "now that she is making steps to follow through with what they asked."

Experts say Spears had better have a Plan B.

Their advice? Show up in person to today's 1:30 p.m. hearing and throw yourself on the mercy of the judge that even her own attorney admits she defied. And, oh, yeah - wear underwear.

"I would go in person and offer to take a drug and alcohol test every single day," said Alexandra Leichter, a private judge and family law arbitrator.

"The judge gave her ample opportunity to prove herself, and she screwed up," Leichter said. "She'd better go in and say she was on her deathbed, or bring a doctor's note  . . .  or show some kind of convincing evidence she was incapacitated."

Spears' attorney Sorrell Trope confirmed his client lost custody of sons Sean Preston, 2, and Jayden James, 1, after missing a court-ordered drug test and failing to provide a valid California driver's license for the court.

"We weren't able to prove compliance with what the judge ordered," he told People magazine.

Now, she can, at least for the driver's license. A spokesman for the California Department of Motor Vehicles confirmed Spears was issued an interim driver's license yesterday.

"She was fingerprinted and photographed Monday. She will be issued a formal license in the mail soon," the spokesman, Mike Marando, told People.com.

Judge Scott Gordon ordered the singer to get counseling, parental coaching and submit to random blood and urine tests last month after declaring Spears a "habitual, frequent and continuous" user of drugs and alcohol.

It was Mark Kaplan, the lawyer for Federline, who ratted out Spears, Trope said.

If Spears plans today to insist that it was all a scheduling problem, she may get a lashing.

On her schedule the very night the judge's order to clean up her act was made public was a night out with the girls.

Making matters even worse for the scandalized singer, In Touch Weekly is reporting that a sex tape of Spears, 25, and an unidentified 28-year-old man she met while on vacation in Hawaii last June may soon become public.