WASHINGTON – Despite a sharp increase in the prosecution of terrorism cases just after Sept. 11, 2001, only 14 of the defendants have been sentenced to 20 years or more in prison, according to a study based on Justice Department data.

Of the 1,329 convicted defendants, only 625 received any prison sentence, said the study, released Sunday by the Transactional Records Access Clearinghouse, a data research group at Syracuse University. More than half of those convicted got no prison time or no more than they had already served awaiting their verdict.

The analysis of data from Justice’s Executive Office of U.S. Attorneys also found that in the eight months ending last May, Justice attorneys declined to prosecute more than nine out of every 10 terrorism cases sent to them by the FBI,

Immigration and Customs Enforcement and other federal agencies.

Nearly 4 in 10 of the rejected cases were scrapped because prosecutors found weak or insufficient evidence, no evidence of criminal intent or no evident federal crime.

The report comes at a difficult time for the Bush administration: It is sagging in public opinion polls just before congressional midterm elections. Democrats hope to regain control of at least one house of Congress, and President Bush has urged Republicans to run in part on his record in the war on terror.

“There are many flaws in the report,” said Justice Department spokesman Bryan Sierra. “It is irresponsible to attempt to measure success in the war on terror without the necessary details about the government’s strategy and tactics.”

For instance, Sierra said, prison sentences are “not the proper measure of the success of the department’s overall counterterrorism efforts. The primary goal … is to detect, disrupt and deter terrorist activities.”

Because prosecutors try to charge potential terrorists before they act, they often allege fraud, false statements or immigration violations that carry lesser penalties than the offenses that could be charged after an attack, Sierra said. This “allows us to engage the enemy earlier than if we waited for them to act first.”

TRAC totaled the cases that prosecutors labeled as terrorism or antiterrorism no matter what charge was brought. It found only 14 prosecutions in fiscal 2000. That rose to 57 in fiscal 2001, which ended three weeks after the Sept. 11 attacks.

The figure then soared to 355 in fiscal 2002. But by fiscal 2005 it dropped to 46. And in the first eight months of fiscal 2006, through last May, there were only 19 such prosecutions.

Past critics of administration tactics found both favorable and unfavorable possible explanations.

The sharp decline in prosecutions may show that prosecutors have moved away from “all kinds of secondary infractions” they pursued early on, said Steven Aftergood, director of the Federation of American Scientists’ government secrecy project.

Those early cases drew criticism that Arab-Americans were rounded up based on mere racial profiling.

The small number of long prison sentences shouldn’t be a surprise because “terrorism is actually very rare _ far more people are killed in ordinary street crime,” said James Dempsey, policy director of the Center for Democracy and Technology.

Nevertheless, terrorism poses a risk of catastrophic loss of life, “so agencies must pursue a lot of leads that do not pan out,” Dempsey added. “We can’t blame the FBI for pursuing those leads, but we can blame them and the Justice Department for arresting people and making a big media splash when things don’t pan out.”

Meredith Fuchs, general counsel at the National Security Archive at George Washington University, said the light sentences could mean “we are catching people at the margins, not at the center of the plots.”

“The surge right after 9/11 make sense,” Fuchs added, “but the drop-off so quickly means either a lot of that post-9/11 activity was not necessary or that they haven’t identified key people or that key people in custody aren’t being prosecuted.”

At the penalty trial of al-Qaida conspirator Zacarias Moussaoui, the government acknowledged that it has captured most of the Sept. 11 ringleaders including mastermind Khalid Shaikh Mohammed and operations coordinator Ramzi Binalshibh.

Although prosecutors suggested they might be charged somewhere someday, the government has never disproved persistent allegations they were tortured during interrogations overseas and thus cannot be tried in U.S. courts.

If prosecutions “have been compromised by unlawful interrogation or surveillance, that would be worse than ironic,” Aftergood said. “It would mean the government has performed in a self-defeating manner.”