A suspected drug courier made a daring and elaborately planned raid on an Anne Arundel County foster home Monday night to abduct the infant son he had left on a jet while fleeing authorities two months ago, police alleged yesterday.

Authorities are conducting a nationwide search for William Thomas Forrer, 32, a flamboyant escape artist who police alleged snatched his 9-month-old son Zachary from the home of a Pasadena, Md., foster family.

Police said Forrer, with the help of the baby's mother and two other persons, overpowered an Anne Arundel County social worker and forced her to lead them to the home of the family caring for Zachary. Forrer persuaded the foster family to give him the child by posing as an FBI agent, according to the police account.

Forrer and his companions then fled, police said, after giving the social worker $500 for caring for Zachary and leaving her handcuffed to a tire inside a van.

The social worker, Lynn Martin, said yesterday that Forrer hit her and told her he would kill her and the foster family if they did not release his son.

"He said, 'I guess you already know who I am,' " Martin, interviewed on television, quoted Forrer as saying. " 'I want my baby. I'm really desperate to do this. But I need my baby. That's all I want.' "

Forrer's son had been a ward of the state since Feb. 21 when, police allege, Forrer left him and a diaper bag containing $35,000 on an airplane seat at Baltimore-Washington International Airport. Anne Arundel County police spokesman Richard Molloy said Forrer fled from a Florida-bound jetliner after he realized he was under police surveillance. Molloy alleged that Forrer left three bags of marijuana in the airplane restroom and, pursued by state troopers, ran through the terminal, stole an airport van and escaped.

Forrer, who is wanted for escape from prison, and the child's mother, Joyce Anne Klipa, 27, are being sought on previously issued federal warrants.

Klipa is wanted for allegedly failing to appear before a grand jury that was investigating whether she harbored a fugitive, according to the FBI.

Anne Arundel County police said yesterday that charges against the couple and their two unknown companions have not yet been filed. Authorities are still trying to determine what offenses they could be charged with.

FBI spokesman Andrew Manning said Forrer is "a high liver" who is "known from New York to Miami as an alleged drug runner." Manning said Forrer is suspected of using expensive stolen cars, including a Mercedes-Benz and a Ferrari, to run drugs up and down the East Coast. Forrer has twice been convicted on stolen vehicle charges and twice has escaped from prison in Florida, Manning said.

According to Molloy's account of the incident, Forrer, flashing an FBI badge, confronted Martin as she arrived at her Baltimore County apartment building about 8:30 Monday night. Forrer told her to come with him, and when Martin resisted, Forrer and a male companion forced her into a waiting Mercury Monarch, Molloy said.

Molloy said police believe Forrer's companion, described as a bearded, heavyset man, delivered a dozen roses -- sent anonymously -- to Martin's office two weeks ago. According to Molloy, police believe Forrer and his companions had learned the name of the social worker handling Zachary's case and watched the county social services office that evening so that when Martin emerged with the roses they could see who she was and follow her home. Molloy said police believe they watched Martin's movements for weeks before allegedly abducting her Monday night.

Police said Martin was driven to the Arbutus area of Baltimore County, where she was transferred at gunpoint to a 1972 Ford van. Inside, according to Molloy, was Klipa, Zachary's mother. The four then drove toward Pasadena, in Anne Arundel County, stopping at one point to let Forrer's unidentified male companion out of the van. Molloy said police believe the man got into a yellow Chevrolet Vega, which Forrer and Klipa later allegedly used in their getaway.

Molloy said Forrer then drove the van to the foster family's home, telling Martin that he planned to demand his son at gunpoint. Molloy said Martin, concerned that people would be hurt, talked Forrer into again posing as an FBI agent and taking her in with him.

"He told her, 'If anything goes wrong, you're all dead,' " Molloy said. He added that Martin "was extremely cool given the pressure she was under." The foster parents, whose identies have not been released by police, knew Martin and apparently believed that Forrer was an FBI agent, Molloy said. They turned over the child and the three left without further incident, according to Molloy.

Forrer then drove the van to Mountain Road, a busy Pasadena street, and handcuffed Martin to a spare tire in the back of the vehicle, Molloy said. Klipa then handed Martin five $100 bills and thanked her "for taking such good care of the baby," Molloy said. Forrer, Klipa and Zachary then left the van, Molloy said, and police believe they fled in the yellow Vega, waiting nearby.

A few minutes later, Molloy said, Martin, who managed to get out of the van still handcuffed to the tire, got help from an off-duty Anne Arundel County officer who happened to be driving by with his family.