A 20-year-old Canadian who was enrolled in the Fairfax County branch of Straight Inc. testified in federal court yesterday that he was tied up in car with nylon ropes by his Straight custodian last month but escaped during a traffic jam on the Woodrow Wilson Bridge.

Two other former clients of the Florida-based drug rehabilitation agency told the jury that they were kidnaped, both at their parents' instigation, and forcibly returned to the program after escaping.

The witnesses testified yesterday in U.S. District Court in Alexandria on behalf of Fred Collins of Fairfax, who is seeking money damages from Straight for detaining him in the program for more than four months last year.

The testimony is being heard by the same jury that found two weeks ago that Collins had been held in the program against his will. The jury is expected to begin its deliberations on the issue of damages today.

Collins, 20, is seeking compensatory damages for financial losses he claims were incurred because of his imprisonment in the drug program and punitive damages.

In his opening statement to the jury, Philip J. Hirschkop, Collins' chief counsel, said he planned to show "a continuing pattern" of false imprisonment by Straight staffers, both before and after Collins' stay.

Jeffrey James McQuillen, 20, of Toronto, who was enrolled in the Springfield branch of Straight, described in court his escape from his Straight custodian during a traffic jam on the bridge.

McQuillen, who said he was bound by nylon ropes, said he tried "picking at the rope with my fingernails and biting it," and finally ripped all his belt loops off. When the driver pulled on to the shoulder and crawled into the back seat, McQuillen rolled into the front and scrambled out, he testified.

Arletha Luann Schautteet, 19, testified that after six months in the St. Petersburg, Fla., branch of the program, from October 1981 to April 1982, she was allowed to drive between her job and the Straight facility. "One night I was driving a girl home from night school and I just kept going," Schautteet told the jury.

Four days later, her mother came to the friend's house where Schautteet was staying. "Three people came running out of the bushes," Schautteet testified, "They fought with me for about 30 minutes, grabbing my arms and legs and trying to push me into my mother's car." Schautteet said she was released through the intervention of a lawyer called by her fiance.

Hope Yvonne Hyrons, 19, testified that while her mother was driving her to a doctor's appointment, two "very tall" men who said they had car trouble got in on either side of her. After her father also got in the car, she was taken to Straight, Hyrons testified.

Dr. James Egan, head of psychiatry at Children's Hospital, testified that as a result of Collins' detention by Straight, he exhibits chronic depression, low self-esteem, guilt, paranoia and excessive-compulsive behavior and needs psychiatric counseling.

Dr. John Meeks of the Psychiatric Institute of Montgomery County, testifying as a witness for Straight, said Collins' emotional problems dated back to his childhood and were not induced by his experiences with the drug rehabilitation program. Collins' father, Fred Collins Sr. of Mount Vernon, enrolled him in the program.

Meeks also testified that if Collins was awarded a large sum by the jury, "he might feel exonerated" and say that drugs were not the source of his emotional and family problems.