Jury selection began yesterday in the federal trial of political extremist Lyndon H. LaRouche Jr. and seven associates in Boston on charges of credit card fraud and obstruction of justice, and lawyers involved in the case say it is one of the strangest criminal cases in memory.

The trial, the first criminal case against the LaRouche group, carries immense stakes for the organization, besides the potential five-year prison terms and fines members could face. Several former group members are expected to testify for the prosecution, breaking the organization's strict code of silence for the first time.

If prosecutors can persuade current members to give evidence, experts on the group say, it could damage its cohesive nature, possibly splitting it and prompting a move from its home base of Leesburg, Va.

Yesterday, potential jurors answered a 10-page questionnaire concerning their feelings about LaRouche. The selection could take a month as lawyers choose 12 jurors and six alternates from a pool of 500. The trial is expected to take at least three months what with 11 defense attorneys and the prosecution saying that it will introduce up to 150 witnesses.

This trial has a little bit of everything: mystery witnesses, recanting of testimony, allegations of secret plots involving the CIA and Soviet spies, an international hunt for fugitives, and millions of missing dollars.

"Everybody involved in the case admits it's the most interesting case they've ever had," said Michael Reilly, a Boston lawyer who represents one of five LaRouche-affiliated groups also facing trial.

For starters, there is the LaRouche group's defense. Group members say what they did was legal because the CIA told them to do it -- an ironic assertion because LaRouche for years said the CIA wanted to kill him.

The CIA defense comes in response to charges of obstruction of justice -- involving allegedly burning subpoenaed documents and hiding witnesses to keep them from investigators. LaRouche and his associates say they believed that they were acting on the instructions of top CIA officials who were passing their orders to LaRouche through intermediaries.

One intermediary LaRouche believed was working for the CIA is a LaRouche group consultant, Roy Frankhouser of Reading, Pa., a former Ku Klux Klan leader who once pleaded guilty to dealing in stolen dynamite.

The problem for the LaRouche defense is that Frankhouser and the other supposed intermediary to the CIA -- Frankhouser's longtime friend, former Klan member Forrest Lee Fick -- have told the FBI that they had made up tales to the LaRouche associates about their ties to the CIA. But the defense still insists that the LaRouche group's actions were legal because its members believed the two had those CIA ties and were acting on orders of the government.

Matters have become more convoluted now that Frankhouser, one of the defendants, has denied ever telling the FBI he made up the stories to the LaRouche group. Also, Frankhouser has put several recorded tapes on his telephone in Reading in which he accuses the FBI of distorting his statements and denounces his former Klan friend Fick as a liar.

It will not help the government's case that it has to rely on witnesses like Fick, who for years has put out a racist publication that praises neo-Nazis in Germany.

Another potentially troublesome prosecution witness is Mordecai Levy, a leader of a militant Jewish organization. Levy infiltrated the LaRouche group for years because he believed that it was anti-Semitic, but friends say he sometimes seemed to swing his allegiance to LaRouche.

Among the other oddities in the LaRouche case so far:

In the middle of pretrial maneuvering several months ago, prosecutors, in an apparently unprecedented move legally, forced two of the defendant corporations into bankruptcy to pay $16 million worth of judgments to the government for contempt of court. A federal judge in Boston levied the fines because the group failed to produce subpoenaed documents.

LaRouche initially avoided indictment and stayed in Europe for months before returning a few months ago and -- against the strenuous advice of his attorneys -- volunteering to testify before the grand jury. Based in part on that testimony, the panel promptly indicted him. Sources said LaRouche testified in part because he believed that he could charm the grand jury.

Defense attorneys flooded the courts with about 300 motions to dismiss the charges or make evidence unusable, including highly speculative assertions that the government was after LaRouche because fired White House aide Lt. Col. Oliver L. North was angry with him. A LaRouche group attorney acknowledged that many of their legal assertions required "a suspension of disbelief," and the judge dismissed most of them.

The West German government is scurrying to try to find three fugitive LaRouche associates, from among the 13 indicted, who are charged with bilking financial contributors to the group. They left the country three years ago after the FBI started investigating.

Meanwhile, sources said that group members are preoccupied with the prospect of going to jail and with rumors that the government has an informant inside the cohesive organization. Former group members said that the close-knit group could unravel if members feel abandoned in jail.

LaRouche once made a statement suggesting that he is placing distance between himself and associates who might be convicted.

Commenting on the charge that associates defrauded group contributors, LaRouche said that while there were "substantial irregularities" in these transactions, the responsible party might have been "a volunteer acting under the compulsion of some emotional disturbance."

But LaRouche also said this year that he believes that associates would not cooperate with authorities even in jail. They are clean-living and strong, LaRouche said, not "hedonistic," and are driven by a "higher motivation . . . . Most of them have plenty of stamina."