The bride was wearing a blue and white, '40s-style jersey dress as she stepped gingerly to the metal detector.

The wedding guests had to offer bags for thorough searches. The ushers wore pistols and handcuffs. The best man was a one-time member of the Detroit Purple Gang, while the most famous invitee, Charlie Manson, had to send regrets that he couldn't attend.

It wasn't your typical wedding scene yesterday at the California state prison system's maximum security medical center here. But the nuptial pair, San Francisco insurance broker Jane Frey and Willie Carter Spann, President Carter's eldest nephew, weren't your typical newlyweds.

Spann, serving time for armed robbery, is the self-professed black sheep of the Carter family. But yesterday morning, Spann seemed less the first family's persona non grata and more like any nervous bridegroom. "I'm scared to death," he kept saying to no one in particular. "I can't believe it's finally happening."

For Jane Frey, 41, the wedding capped a romance that inadvertently started last year when she helped negotiate a magazine deal for the 32-year-old Spann. Correspondence led to a first visit in October, then to Spann's proposal in February, and finally to yesterday, when Frey found herself driving to Vacaville singing, "Get me to the prison-on time."

"When I met Willie, I was amazed at how intelligent and articulate he was," says Frey, a New Jersey-born Sorbonne graduate who sells commercial property insurance. "I knew I was going to marry him the minute he asked."

Once past the photographers and security checks at the prison gate, Frey and her allotted eight guests (none of the Carter family) assembled in the Vacaville visiting room, best known as the site where a handful of prisoners founded the Symbionese Liberation Army some years back. For the wedding, however, the chamber became a makeshift dressing room.

Spann slipped into a white, loosesleeved Indian shirt he borrowed from a photographer, tucking it nervously into his neatly pressed blue prison denims while Frey carefully adjusted her simple bouquet of three white roses.

"This is going to mean a whole new life for me," Spann enthused.

The way he tells it, Spann, the only son of presidential sister Gloria Carter Spann's first marriage, was neglected as a child and in jail by the time he was 12. "The only time I got attention was when I did something wrong," he recalls. "So I did lots of things wrong."

Much of his life since then has been spent in various jails since he has kept "in constant trouble all his adult life," as President Carter put it when Spann became an issue in the 1976 presidential Carter put it when Spann became an issue in the 1976 presidential campaign. Spann says his criminal resumes included burglary, pimping, drug dealing and heroin addiction before he was sentenced to his current prison term for armed robbery of a San Francisco gay bar three years ago.

Though he remains estranged from many of his kin (grandmother Miss Lillian writes monthly), Spann's first family ties have made him a potential target for thugs trying to carve a prison reputation; so authorities have kept him locked in a tiny maximum-security cell near the cells of such other notables as Juan Corona, Charles Manson and yesterday's best man, Norman St. Martin of the Purple Gang.

By yesterday, however, the bitterness of family estrangement dissolved into hopes for the future. "My family is here," Spann announced to the guests in the prison courtyard. "Nobody's ever looked at me before and been really glad for me when something good like this was happening. I didn't know that there could be love in life the way I'm seeing it now."

The Rev. Bill Hausler from Vacaville's Trinity Christian Center then called the guests together. As armed guards watched from the sidelines, the couple softly intoned the simple wedding vows. "They seem to care very strongly about each other," he said. "That's the only thing I look for."

After applause and a round of traditional handshakes and kisses, Willie Spann pulled the minister into a group wedding picture. "I want my family to know this was respectable," he joked.

Soon after, the guards explained they had an upcoming noon meal to monitor and begun ushering the guests back out the gates, leaving the groom a lonely figure in the empty visiting room. "This is the hardest part," said the bride sadly, "having to separate now, on the most important day of our lives."

The separation is temporary, added Frey, and the presidential nephew will move into his wife's San Francisco apartment after his scheduled Dec. 24 parole, and then take up courses in electronics. "From then on," said the new Mrs. Spann, "we can grow old and have fun together."

For all the extenuating circumstances surrounding this most unusual wedding, some moments differed little from any wedding. The matron of honor cried. The bride's voice quivered when she took the final vow, and as the groom leaned into his first nuptial kiss, he softly whispered, "I love you." CAPTION: Picture 1, Willie Carter Spann in 1976 . . .; Picture 2, . . . and bride Jane Frey yesterday; AP photos