A federal informant testified yesterday that former WRC radio sports talk show Daniel L. Snyder, charged with running an illegal sports bookmaking operation, told her that referees were taking payoffs to fix professional basketball games.

Mae Sullivan testified that while she worked as a bookie, or bet-taker, in an Arlington-based FBI undercover sports bookmaking operation, Snyder gave her in advance the correct victory margin, shown as the "point spread" or "line," for six professional basketball games that he claimed were fixed in February and March 1979.

"He told me that referees fouled players in the first part of the game," Sullivan testified at Snyder's trial in U.S. District Court in Alexandria.

"He would tell me the games that were fixed and within the point spread that they were supposed to win, which enabled me to manipulate my point spread so that I could give it to my other customers," Sullivan said.

A National Basketball Association official said yesterday that its own internal investigation found no substance to the fixing allegations. "We have no reason to believe there is anything to the allegations," the NBA official said.

For six months, beginning in December 1978, Sullivan along with three undercover FBI agents, who went by the nicknames "Tony," "Johnny," and "Art," posed as sports bookmakers, Sullivan testified.

Operating out of an Arlington apartment equipped with two telephones, Sullivan and the agents took "layoff" bets from 10 other bookies in the Washington area, paid off winning bets, allegedly including $5,000 to Snyder, and on occasion visited other bookies who had fallen behind on payments, according to court testimony.

Saul Glickstein, who pleaded guilty to a related charge in the case and testified for the government at Snyder's trial, said that an undercover agent once threatened "to bounce my head against the wall like a basketball" when the self-described bookie fell behind in payments to the FBI operation. Glickstein testified he took the threat as a "joke."

Sullivan also testified that during one of many telephone conversations with Snyder during the operation, he told her that he was talking to White House press secretary Jody Powell on another line and that Powell was one of the many prominent people who placed bets with him.

She said Snyder boasted that among his customers were judges, including a U.S. magistrate from Northern Virginia, congressmen and senators. "He told me that he would have the biggest bettors in town . . . and that during football season he would make me a wealthy woman," Sullivan testified.

But instead, she testified, Snyder ran up more than $1,000 in losses, gave her three checks that bounced and generally failed to bring in the big business that he promised.

Joel Finkelstein, one of Snyder's lawyers, described his client in an opening statement to the jury as a "sick . . . compulsive . . . neurotic bettor." In outlining a defense based on entrapment, Finkelstein said that Snyder's gambling addiction forced him to masquerade as a bookie with big connections so that Sullivan would let him place bets with her operation.

He dismissed Snyder's statements about the fixing of NBA games as "puffery," noting that gamblers often make exaggerated claims to one another.

Under cross-examination, Sullivan acknowledged that gamblers, including herself, often tried to con each other. For instance, she said she didn't believe Snyder when he said he was talking to Jody Powell.

But, she said, "Danny (Snyder) knew a lot of people." She testified that he was once the promoter for an athletic contest at the University of Maryland's Cole Field House in which several congressmen and senators participated.

A middle-aged woman who spoke in a deep voice, Sullivan, now an Arlington housewife, said she began cooperating with the FBI after she thought someone was trying "to set me up." She said she had known Snyder for many years and contacted him because he had bet with her in the past.

Snyder was suspended from his once-a-week betting-oriented show, called "Who's Gonna Win on Sunday," late last year, a WRC spokesman said. "We were shocked to find out about his alleged involvement," the spokesman said.

Snyder, 39, an Alexandria resident, is charged with conspiracy and violating federal racketeering laws in 11-count indictment. The prosecution will resume its case today.