The man accused of raping a Silver Spring woman and then throwing her from a bridge into the Patuxent River was arrested early yesterday by Montgomery County police after his brother lured him into a trap, county officials said.

The arrest ended an intense 10-day search for Richard Dale Baumgardner, 25, of Clarksburg.

His brother, Wayne David Baumgardner, 28, of Bethesda, apparently told Richard Baumgardner that he would help him flee if he hid in the trunk of a car. Instead, he delivered the suspect to the Wheaton police station shortly after midnight, officials said.

Wayne Baumgardner agreed to turn in his brother after he was summoned to appear before a county grand jury and answer questions under oath about his brother's whereabouts, officials said. They said that five persons, including some relatives and acquaintances of Baumgardner, appeared before the grand jury Thursday.

Less than five hours after that session ended, Richard Baumgardner was in police custody.

Baumgardner, who was unarmed at the time of his arrest, surrendered without a struggle when the trunk of the car was opened and he found himself surrounded by about 10 Montgomery County police officers, police said.

"He thought he was being taken to a bus station," police spokesman Phil Caswell said.

Baumgardner is being held without bond at the Montgomery County Detention Center in Rockville. He is charged in Montgomery County with attempted murder, kidnaping, rape and felony theft. An arrest warrant for Baumgardner has also been issued in Howard County charging him with abducting a woman at knifepoint, robbery and assault. That woman escaped without serious physical injury.

At the bond hearing yesterday before District Judge Louis D. Harrington, Matthew Campbell, assistant state's attorney, described Baumgardner as a "dangerous person" who should be held without bond.

Campbell told the court that the case against Baumgardner is "extremely strong."

"Baumgardner has been readily identified by the victim and by other people who can place him in her car," Campbell said in court. He said that Baumgardner had admitted to other people that "he threw the victim off the bridge into the Patuxent River and indeed waited until he heard the splash before he got back into her car."

A preliminary hearing for Baumgardner has been scheduled for Feb. 21.

The Silver Spring woman, although gagged and bound throughout her ordeal with handcuffs, managed to swim to shore, flag down a passing motorist and notify police. Arrest warrants for Baumgardner were issued after police found his truck in the parking lot of the Wheaton Plaza Shopping Center, where the woman was abducted late Jan. 6 in her own car. She was then taken to a motel in Howard County, where she was raped, and back to the Rocky Gorge Bridge over the Patuxent, where she was thrown into the river, police said.

"He had handcuffed her to the steering wheel part of the time," Campbell said. "She tried a couple of times, when he stopped the car and got out for a few minutes, to attract the attention of others by blowing the horn but he heard her and rushed back to the car."

Police Detective Bill Campbell said the woman's hands were handcuffed behind her back when she was thrown from the bridge, but she was able to swim on her back to shore.

Campbell said the rape victim, described as "slender but fit," was held captive for nearly three hours after she was abducted with a six-inch hunting knife.

The woman, 30, a single professional whose identity has not been released by police, was notified about 3 a.m. yesterday that Baumgardner had been arrested. "She was greatly relieved," said Sgt. Harry Geehreng.

The arrest climaxed a massive effort by Montgomery County police working in cooperation with the state's attorney's office and the grand jury.

"Efforts that detectives made . . . and the pressure they kept on the family and relatives of the suspect was critical in the apprehension," said Montgomery County Police Chief Bernard D. Crooke. "The detectives had everything worked out, and then went to the grand jury to get it under oath."

"What happened was that the police came to us last week, and we worked with them and the grand jury to bring in witnesses in the case," said State's Attorney Andrew L. Sonner. "After several witnesses testified before the grand jury, we were able to sit down with certain witnesses and the police and secure an agreement to have him [Baumgardner] produced."

Wayne Baumgardner, who is married and has three children, could not be reached for comment last night.

Bill Campbell, one of the chief police investigators in the case, said that Baumgardner has spent the last 10 days in the general metropolitan area, as far as investigators can tell.

During that time, Campbell said, "we had information about certain individuals who were aiding and assisting him in eluding apprehension by police."

Police also had information that Baumgardner was being transported around the area by persons "who put him in the trunk of their car" to escape detection, Campbell said, so Baumgardner apparently assumed he was "taking another ride in the trunk" when he was driven to the police station.

Officials gave no indication yesterday that action would be taken against any of those persons.

Both of the Baumgardner brothers are from southern Howard County, an eclectic rural area of aging mansions, frame farmhouses, brick ranch-style homes and raw new town houses scattered among estates offering goats for sale, registered puppies and kittens, pleasure horses for rent and firewood.

The Baumgardner family home, near the Brighton Dam recreation area, is a fairly new brick and white siding ranch house with a barn. There are a sport truck and two covered pickups in the driveway.

One neighbor said, "I'm just glad Baumgardner is in custody. I was afraid to let the kids play outside. Rumors were rampant" that Baumgardner had been seen in the neighborhood in the days since the rape.

Both Richard and Wayne Baumgardner attended Glenelg High School, school officials said.

*In 1978, Richard Baumgardner was sentenced to 10 years for rape and 90 days for possession of drugs, parole records show. He was paroled from the Maryland Correctional Training Center in August 1984.

Since that time, Baumgardner, for the most part, has been unemployed and "living out of his truck," according to Detective George G. Neville Jr.

Yesterday, Chief Crooke said he was relieved that Baumgardner was in police custody.

"I had the true fear that there might be more victims, and that the next one might not survive . . . and it was inevitable that there would be a next victim."