In their case against former Enron Corp. chairman Kenneth L. Lay, federal prosecutors are alleging that he was part of a broad conspiracy to defraud investors while charging him mostly with discrete, easier-to-prove crimes such as lying to company employees and to his personal bankers.

The strategy, a classic use of the powerful federal conspiracy statute, allows prosecutors to blame Lay for Enron's dramatic slide into bankruptcy in December 2001 without having to explain every accounting trick, legal analysts say. Instead, the prosecutors can focus on Lay's signature on loan agreements and his words in tape-recorded conference calls to analysts.

But the fact that Lay is charged with far fewer and, on the surface, less serious offenses than the two other former Enron officials indicted with him may be viewed by jurors as a weakness in the government's case, some analysts say. Lay pleaded not guilty Thursday.

The 53-count indictment charges former Enron chief executive Jeffrey K. Skilling and former chief accountant Richard A. Causey with making false SEC filings dating back to 1999, engaging in insider trading and playing a role in the off-the-books partnerships that hid Enron's staggering debt for years. Lay is charged with 11 of the counts -- the overarching conspiracy and 10 wire fraud, securities fraud, bank fraud and false statements counts tied specifically to lies he allegedly told to company employees, analysts and his personal bankers, most in the fall of 2001. Skilling is charged in 35 counts; Causey in 33. Skilling and Causey have also pleaded not guilty.

"There's nothing about this indicating that Ken Lay was a kingpin," said former federal prosecutor Jacob S. Frenkel. "Even though Lay is higher up in the hierarchy, the indictment suggests that the fraudulent activity centered around Skilling. To the extent that Ken Lay was the ultimate target, the fact that they couldn't say more about him is as telling as the charges they brought."

The indictment contends that Skilling, who was running day-to-day operations at Enron long before he took over as chief executive, stood at the center of a wide-ranging conspiracy to inflate Enron's stock price and hide debt by using secret agreements, accounting gimmicks and business partnerships carried off the company's balance sheet starting in 1999.

Causey, the chief accounting officer during that period, furthered the scheme by conducting meetings at which Enron's financial targets were discussed and by entering into a secret deal with Enron finance chief Andrew S. Fastow to guarantee Fastow would never lose money in his personal dealings with the company in exchange for his helping disguise its debt, prosecutors claim.

Lay played a more narrow role, according to the indictment, "taking control" of the conspiracy after Skilling abruptly departed Enron in mid-August 2001 and making optimistic public statements to investors, analysts and employees at a time when he knew Enron's finances were headed toward collapse.

Lay is cited in seven of the 22 "overt acts" in support of the alleged conspiracy -- all of them from September through November 2001. (Causey is cited in 16 and Skilling in 13.) Lay's attorney Michael Ramsey says Lay is being blamed unfairly for the company's collapse and the actions of a few greedy underlings.

"The case against Lay seems to pale in comparison with Skilling and Causey," said Duke University law professor James D. Cox. "If they try all these guys at the same time, they run the risk of the baby, Ken Lay, being thrown out with the bathwater."

This week's verdict in the criminal case against the former leaders of Adelphia Communications Corp. shows that there are no guarantees. In that case, a Manhattan-based jury convicted Adelphia founder John J. Rigas and his son Timothy, the former chief financial officer, of securities and bank fraud but deadlocked on another son, Michael, after prosecutors were unable to show he was personally involved in concocting accounting schemes and looting the cable television firm. Jurors also acquitted a lower-level executive, Michael C. Mulcahey, who did not personally profit from the schemes.

"A conscientious jury makes those kinds of distinctions based on level of culpability. Ken Lay should be hugely relieved by the Adelphia verdict," said Columbia University law professor John C. Coffee Jr.

One of the differences among the defendants is that only Skilling and Causey are charged criminally with insider trading, although the Securities and Exchange Commission has brought civil charges against Lay, Skilling and Causey, alleging that they dumped millions of dollars in stock as Enron imploded.

Legal analysts said the difference almost certainly stems from the fact that Lay appears to have a strong defense against insider trading. He and his attorneys have argued that he sold stock only when he was forced to by the terms of his loans and that he passed up opportunities to sell more.

One possible problem with the case against Lay, analysts said, is that much of the evidence will come in the form of testimony from the five alleged conspirators who have already cut deals with the government, most prominently Fastow. "One thing that's missing here is the smoking gun e-mail. There's going to be a disproportionate reliance on the cooperating witnesses," said former federal prosecutor Kirby D. Behre. "Until you hear those statements on the stand, you just don't know how strong the case is."

In addition, several of the securities and wire fraud charges will require prosecutors to prove not only that Lay's statements to analysts and employers were objectively false but also that he was deliberately trying to mislead. That's because the law allows executives to engage in "puffery," or talk up their company's potential, as long as they don't actively mislead.

For example, "there is nothing wrong with telling the public that your muffin company is a great investment because people can eat muffins for breakfast, lunch, dinner and dessert. That's just puffing. But to say that your muffin company's orders are on a steady increase when they are down, well, that's fraud," said Steven M. Cohen, a former federal prosecutor.

In Lay's case, his attorneys may also be able to use the fact that he has not been criminally charged with any knowledge of wrongdoing before September 2001 to argue that he, too, was duped and was simply doing his best to save the company he founded.

"There is at least a plausible case that he is a true believer who went down with his ship," Coffee said.

Washington Post staff writer Carrie Johnson contributed to this report.

Kenneth L. Lay and wife Linda leave the federal courthouse in Houston after his plea.