LOS ANGELES – As a top fundraising official on Senator Clinton’s 2000 campaign takes the witness stand in his own defense this morning, jurors are expected to get a detailed, if one-sided, story about the August 2000 concert at the core of the case.

It will be a pivotal moment for the former fund-raising chief, David Rosen, who will seek to convince the jury that he had no idea that the gala’s backers spent $700,000 more than was reported to federal officials.

Perhaps the most striking aspect of Mr. Rosen’s trial thus far is the number of key figures in the case that the jury has not heard from and probably never will.

Neither side is expected to call the former Internet entrepreneur who bankrolled the gala, Peter Paul, or the well-connected organizer of the star-studded event, Aaron Tonken. Their absence may be puzzling to the jury, which has heard a great deal about Paul and Tonken from other witnesses.

“They’re the elephants in the room,” an attorney familiar with the case said. “The jury may ask: ‘Where were they?’ That’s the risk,” the lawyer, who asked not to be named, said.

Legal analysts said the government likely declined to call Paul and Tonken because of their checkered pasts and obvious credibility problems.

“If they look sleazy, the government case kind of looks sleazy,” a law professor at George Washington University, Stephen Saltzburg, said.

Paul is a four-time convicted felon who recently pleaded guilty to securities fraud involving the same publicly traded company that was listed as the lead underwriter of the gala, Stan Lee Media.

Tonken is serving a 63-month sentence on federal fraud charges related to his handling of funds from celebrity charity events similar to the August 12, 2000, gala.

The defense could call Paul or Tonken, but might find they add to the weight of testimony suggesting that Mr. Rosen knew about the excess costs.

“You never know what you’re going to get,” a Staten Island lawyer who teaches trial tactics at Columbia University and the Benjamin N. Cardozo School of Law, Thomas Bello, said.

Instead, Mr. Rosen’s attorneys are mounting a variation of an “empty chair defense,” which seeks to lay the blame on a third party without the inconvenience of having to hear that person’s story. Mr. Bello said the “empty chair” technique rarely works because the judge usually instructs the jurors that the only issue they are to consider is the guilt of the defendant in the courtroom. “It’s usually a losing strategy,” he said.

While much of the testimony from other witnesses has involved Paul and Tonken, the jury has learned about the history of the two men in a disjointed way. The defense played an ABC News story that mentioned Paul’s criminal record and that he departed for Brazil as his company, Stan Lee Media, ran aground.

The first warning the jury got of Tonken’s troubles came when a woman who used to work for Tonken gave his current location as “incarcerated.”

Tonken and Paul are eager to testify. Tonken has even written a 485-page book, “King of Cons,” much of which is devoted to the gala and his interactions with the Clintons and their retinue. The jury will hear none of that. Books, as a rule, are inadmissible as hearsay.

It also appears that a secretly recorded audiotape of Mr. Rosen that figured prominently in the press coverage of the case will never be discussed in detail in front of the jury. They were told of the existence of the tape, which was made by a Democratic fund-raiser who is Senator Kennedy’s brother-in-law, Raymond Reggie. However, prosecutors won an order from the judge to keep the defense from discussing the contents of the recording.

In his testimony, Reggie said that the night before the gala, Mr. Rosen had a loud argument about the costs of the event with one of Mrs. Clinton’s closest aides, Kelly Craighead. Reggie said that as the pair squared off, two other aides to the then-first lady were also present, the White House social secretary, Capricia Marshall, and Mrs. Clinton’s scheduler, Patricia Solis Doyle. While Ms. Craighead has been mentioned as a possible witness, none of the aides has yet appeared at the trial.

It is possible that some of the missing witnesses could still be called, either by the defense or the prosecution in rebuttal. The attorneys involved have declined to discuss their trial strategy. However, both sides have indicated that the case will likely go to the jury in the next day or two.

Also absent from the witness box thus far is the producer of the concert, Gary Smith. Reggie testified last week that Tonken and Mr. Rosen complained that much of the event’s cost was due to Mr. Smith’s fees. According to Reggie, Tonken and Mr. Rosen said Mrs. Clinton insisted on Mr. Smith, who has produced a host of Democratic conventions and televised awards shows.

In an interview, Paul recounted a meeting he had with Mr. Smith, Mr. Rosen, and Tonken at Le Dome restaurant in West Hollywood several weeks before the gala. He said the four discussed Mr. Smith’s fee of $850,000.”I almost fell off my chair when he said he wanted 850 grand,” Paul said.

Proof of such a discussion could undermine Mr. Rosen’s case, because he is insisting that he knew of no more than about $500,000 spent on the entire gala.

Mr. Smith’s office referred questions to his attorney, who did not return a call seeking comment. However, a source familiar with the case said the acclaimed producer does not recall either Tonken or Mr. Rosen being present at the meeting at Le Dome.

Paul said he suspects that Mr. Smith has not testified because he could implicate Mrs. Clinton in the underreporting. Paul and Tonken both contend that Mrs. Clinton persuaded Mr. Smith to drop his total price by $50,000. “She called him that night and he lowered his fee,” Paul said.

However, a Chicago fund-raiser involved in planning the gala, James Levin, testified that he was the one who asked Mr. Smith for the discount. Levin, too, has credibility issues. He recently agreed to plead guilty to a scheme involving bribery and minority contracting fraud. Mr. Rosen’s attorneys have branded him a liar.

Paul, who has allied himself with political opponents of the former first lady, said the discrepancy about who knew about Mr. Smith’s fee and who negotiated it makes Mrs. Clinton the most central witness not to take the stand. “The testimony shows she was involved,” he said. “Without question, Hillary is the key witness.”

Paul also noted that even after he filed a lawsuit that included canceled checks and other documentation of the $1 million-plus in expenditures made for the event, the committee that sponsored the gala sent a letter to the Federal Election Commission reiterating a figure of about $401,000 in so-called in-kind gifts.

An attorney for Mrs. Clinton, David Kendall, declined to respond yesterday to Paul’s assertions. Paul’s civil suit is pending in a California court.