A federal jury in Alexandria found yesterday that a Florida-based drug rehabilitation agency held a 19-year-old Fairfax County man against his will, but that he had not suffered undue physical or emotional damage while in the agency's program.

After deliberating about 90 minutes, the six-member civil jury reported to U.S. District Court Judge Albert V. Bryan Jr. that they agreed with Fred Collins' assertion that Straight Inc. had falsely imprisoned him in its St. Petersburg facility and, briefly, in its new Northern Virginia facility in Springfield.

The jury dismissed additional contentions by Collins that he was assaulted and made to suffer emotional distress while in the drug program.

A second trial, before the same jury, will be held May 24 to determine whether Collins, who is now 20, should be awarded damages. He is seeking $750,000.

David Fudella, one of Collins' attorneys, called the verdict "a 100 percent victory . . . . We didn't really expect to get" a finding of injury. Fudella and Philip J. Hirschkop, Collins' chief counsel, are representing another former Straight client who has filed suit in Fairfax Circuit Court also alleging false imprisonment.

Straight attorney Ronald Goldfarb downplayed the verdict as a "technical victory," saying that Collins had "won the procedural question, but lost the substantive . . . .

"We can live with the notion that we have to let adult participants in the program walk out, even if they walk into the traffic," said Goldfarb.

Collins claimed he was coerced into entering the program after eight hours of continuous pressure from staff members, that he was held against his will for more than four months in the St. Petersburg facility and that during that time he was subjected to continuous physical and psychological harassment.

Collins said he escaped two days after being transferred to the Springfield facility by throwing a table through a kitchen window of his home, where he was spending the night. His brother George, 16, who became Straight's star witness, is still in the local program.

Straight attorneys argued that Fred Collins enrolled of his own accord and could have withdrawn in accordance with program procedures. "Instead," said Goldfarb sarcastically, "he blew out a window like Captain Marvel."

Defense attorneys also denied any physical or emotional mistreatment of clients, as participants in the program are called. In testimony Wednesday, Straight's national clinical director, Miller Newton, said that in some instances clients had been kept at "marathoning" rap sessions for as long as 70 hours, but he said the practice has been discontinued.

After Collins fled from Straight last October, he said, he sought to get his brother George out of the program, too, in the belief he was being held involuntarily. George Collins, testifying on behalf of Straight, broke down on the stand during his testimony Wednesday. He told the jury that he and his brother had often smoked marijuana and hashish together.

"Would you like to speak to your brother?" Hirschkop asked him.

"No," said George Collins, then added brokenly, "I don't think he'd listen."

Lawyers for both sides referred to the bitterness of a divided family. Goldfarb called the case "a tale of two brothers" and denounced Fred Collins as a man whose "idea of brotherly love" was "to take his 13-, 14-year-old brother to the park and get him stoned."

In their closing arguments, Straight attorneys portrayed Collins as "a con and a faker," while Collins' attorneys compared Straight to a cult.

Hirschkop stressed the door locks, barred windows and alarm systems with which Straight facilities and foster homes are equipped. He asked the jury several times, "Why was it necessary, if Collins could leave any time?"

"This program preaches that they teach love; they teach hate," Hirschkop argued.

Newton said Straight would not decide whether to appeal the verdict until after the question of damages is settled. "If they only award a couple of thousands dollars, which won't even cover Hirschkop's legal fees," he said, "we'll take it as a sign they think we just need to change our rules."

A few similar suits have been filed against Straight elsewhere, but none has gone to trial.