But as Mr. Fortier's release on Friday approaches, the deal cut to secure his testimony against Timothy J. McVeigh and Terry L. Nichols is again gnawing at some of the survivors and relatives of the victims. They worry about a possible future threat posed by Mr. Fortier, 37, and the undisclosed terms of his release, in particular whether he will gain federal witness protection.

''It makes me nervous, it angers me, it frustrates me,'' said Dot Hill, who was working for the General Services Administration in the Alfred P. Murrah Federal Building on April 19, 1995, and credits her survival to leaving her desk for coffee just as the bomb exploded.

''It's an agreement we have to stand by,'' Ms. Hill said in a telephone interview, ''but it puts us on high alert again.''

A lawyer for Mr. Fortier said ''the government is concerned'' about the release as well.

''I am not able to answer questions on that,'' the lawyer, Mike McGuire, said of Mr. Fortier's possible inclusion in a witness protection program.

But, he added, ''there's a real fear that some of these victims are still angry. That's why the government is concerned.''

Mr. McGuire was appointed by a court and said he left Oklahoma City for Tulsa in 1996 after repeated harassment for taking the case.

The federal Bureau of Prisons sent a brief notification to survivors and victims' families this week that Mr. Fortier would be released on Friday after serving 10 1/2 years of his 12-year sentence. A spokeswoman for the bureau declined to provide particulars of the release, respond to questions or even confirm that the letters went out. The United States Marshals Service and Justice Department also refused to comment.

Mr. McGuire would not say where Mr. Fortier had been incarcerated or where he and his wife, Lori, who also testified and has been living in Arizona with their two children, would go now. He described Mr. Fortier as ''tremendously thrilled with the prospect of finally being released'' and ''excited about his future.''

''He's going to put all his resources into providing for his family,'' Mr. McGuire said.

He said the Fortiers would not speak to reporters. Reached by phone, Mr. Fortier's mother, Irene, in Kingman, Ariz., said she had nothing to say and hung up.

Mr. Fortier and his wife had advance knowledge of the plot by Mr. McVeigh and Mr. Nichols to bomb the Federal Building in retaliation for the federal siege of the Branch Davidian complex near Waco, Tex., in 1993, the Fortiers' testimony later showed.

As far back as the summer of 1994, some nine months before the truck bombing, Mr. Fortier testified, Mr. McVeigh, an old Army buddy, ''told me they were planning on bombing a building.''

A few months later, Lori Fortier testified, Mr. McVeigh sat in their trailer home and diagrammed the bombing and on a later occasion set up 12 soup cans to show how he would rig the barrels of explosives.

Mr. Fortier also testified to transporting stolen weapons that helped finance the scheme.

With his wife, he initially lied to F.B.I. agents about their involvement. But after negotiations in the face of charges that could have sent him to prison for 23 years, he agreed to plead guilty to four counts involving transporting stolen weapons and concealing the conspiracy and become the star witness in the trials of Mr. McVeigh and Mr. Nichols.

Mr. McVeigh was convicted in the bombing and executed in 2001. Mr. Nichols is serving life without parole.

While unease over Mr. Fortier's release had been on the minds of survivors and relatives of victims for months, the Bureau of Prisons notification that reached many families on Tuesday caught them by surprise.

''I knew it was coming up, but I didn't know it would be the day before my birthday,'' said John Cole, who lost two godsons in the blast.

Mr. Cole said he considered Mr. Fortier and his wife culpable for not exposing the scheme. As a result, he said, ''they should be right up there with Terry Nichols.''

Ms. Hill, the survivor who took the coffee break, said she ''was fine'' with Mr. Fortier's plea bargain at the time it was reached, ''but now that I know he's wandering around, I'm wondering, are they monitoring him because of his past and beliefs?''

''We don't know if any of that stuff has changed,'' she said.

Ken Thompson, external affairs director of the National Memorial Institute for the Prevention of Terrorism, the organization in Oklahoma City formed to commemorate the victims, said he understood the consternation but did not fully share it.

''Most people understand that if it wasn't for him as a witness we might not have had these verdicts,'' said Mr. Thompson, whose mother was killed in the bombing.

Photo: Michael J. Fortier in 2004 after testifying against Terry L. Nichols. (Photo by Sue Ogrocki/Associated Press)