WASHINGTON, July 19 — Since December, when the government indicted Zacarias Moussaoui as the
first man charged in the Sept. 11 attacks, an unusual gulf has opened between what prosecutors have
charged in court and what investigators are saying privately about what they can prove about him.

Prosecutors have charged that Mr. Moussaoui played a direct role in the Sept. 11 hijackings, and some officials
have said they believe he was supposed to be on one of the four planes. But investigators now say the evidence
is not so clear. In fact, they say they believe he may been in the United States to take part in a different plot.

That gap has opened wider in recent days with Mr. Moussaoui's rambling, combative and often confusing
statements in court. He has declared his allegiance to Al Qaeda and asserted that, if allowed to plead guilty, he
would provide a grand jury with an authoritative insider's account of the hijacking plot — even though at other
points he said he was not involved.

If the judge in his case, Leonie M. Brinkema, allows Mr. Moussaoui to plead guilty at a hearing scheduled for
Thursday, Mr. Moussaoui would follow John Walker Lindh, the Taliban warrior, in short-circuiting the
prosecution. If that happens, each case would have begun with broad assertions that were never proven in
court.

Government officials say they have no direct evidence that Mr. Moussaoui had a role in the hijackings. From
the beginning the evidence has been circumstantial. Now, some government officials, in interviews, are saying
that prosecutors overreached when they charged that Mr. Moussaoui was a direct participant with Osama bin
Laden and Al Qaeda in the conspiracy to kill thousands of people on Sept. 11.

With Attorney General John Ashcroft's counterterrorism team anxious to demonstrate its aggressive approach,
federal prosecutors have dismissed the internal criticisms, saying that the case against Mr. Moussaoui is strong
and that prosecutors had won convictions in jury trials with less evidence than they have against Mr.
Moussaoui.

But Mr. Moussaoui's erratic recent performances in court proceedings have upset the Justice Department's
effort to bring him to trial in an orderly legal process. Instead, Mr. Moussaoui has managed to raise even more
doubts, not only about his emotional and mental competence to stand trial and act as his own lawyer, but also
about whether someone with his apparent instabilities could provide a credible account of his own activities.

Government trial lawyers and F.B.I. agents often disagree about the weight of evidence in criminal cases, but
usually it is the Federal Bureau of Investigation that is arguing for a tougher charge. In this case, some
prosecutors have said that the F.B.I. has been especially eager to depict Mr. Moussaoui as a minor figure, in
part, because the bureau hoped to dampen the controversy about whether it acted properly last summer, when
it refused to seek a warrant to search Mr. Moussaoui's laptop computer. The computer was not searched until
after the Sept. 11 attacks.

The government has yet to produce a witness against Mr. Moussaoui. What they do know is that he received a
wire transfer from Ramzi bin al-Shibh, a Yemeni who, according to the indictment, acted as a financial conduit
for the plot. In addition, Mr. Moussaoui's movements in the months before he was arrested were almost
identical to those of the 19 hijackers.

But investigators have said they have failed to find evidence that Mr. Moussaoui ever met Mohamed Atta, the
plot's ringleader, or any other hijacker — or that he communicated with any of them by e-mail, telephone or
letter. Still, Mr. Moussaoui's associate, Hussein al-Attas, has told the authorities that Mr. Moussaoui had said it
was acceptable to kill civilians who harmed Muslims.

Investigators have said they have no precise understanding of why Mr. Moussaoui entered the United States,
although they are convinced he was a Islamic militant who arrived to take part in some kind of terror operation.
The investigators have speculated that whoever recruited him may have not told him anything about the
operation he was to take part in.

Some officials still suspect that Mr. Moussaoui was meant to be the 20th hijacker on Sept. 11 and was
recruited late in the plot when Mr. al-Shibh failed to obtain a visa to enter the United States. If so, he would
probably have been a fifth man on the hijack team that seized United Airlines Flight 93, which crashed in
Pennsylvania with four hijackers on board; the other planes were comandeered by five hijackers. But this
remains little more than a suspicion.

Lately, some other investigators suspect that Mr. Moussaoui might instead have been recruited for a different,
still unknown, operation, speculating that the Sept. 11 hijack teams had already been selected before Mr.
Moussaoui entered the United States. Because he had taken flight lessons and had information in his computer
about crop-dusting aircraft, these investigators suspect that he was meant to take part in an attack involving one
of those planes.

In his court appearance this week, Mr. Moussaoui's often ranting statements seemed to support that theory. He
confessed that he was part of Al Qaeda, was loyal to Mr. bin Laden and had joined in terrorism conspiracies.
But he repeated his claim that he had "no participation" in the Sept. 11 conspiracy.

Nonetheless, Mr. Moussaoui, who is acting as his own lawyer, has offered to testify before a federal grand jury
to reveal what he knows about the Sept. 11 conspiracy and Al Qaeda.

But prosecutors and the judge in the case have treated his offer with skepticism, especially given his initial
demand — now dropped — that the appearance be televised and that he be accompanied into the jury room
with a Muslim lawyer of his choosing.

Edward B. MacMahon, one of the team of court-appointed lawyers that Mr. Moussaoui has tried to dismiss,
said in an interview that in the course of representing Mr. Moussaoui, the Justice Department had never
approached the defense team with a request that Mr. Moussaoui submit to an interrogation or consider a plea
bargain that would require his cooperation.

That, Mr. MacMahon said, suggested that the department understood that Mr. Moussaoui was a low-level
conspirator who knew little, if anything, about the terrorist network.