Washington ? The FBI has been seeking prosecution of international terrorism cases at six times the rate it did before Sept. 11, but more than half of those cases considered by federal prosecutors never made it to court, Justice Department records show.

In the year before the attacks on New York and Washington, FBI agents sent 10 international terrorism cases a month to U.S. attorneys for prosecution, according to the records obtained by Syracuse University’s Transactional Records Access Clearinghouse (TRAC). In the first six months after the attacks, they sent 59 a month.

The records reflect the intense FBI focus on anti-terrorism investigations after Sept. 11, but they also show prosecutors declined to file charges in 60 of the 98 FBI anti-terrorism cases they considered from last October through March. The prosecutors did not reach a decision during the period on all of the more than 350 cases referred to them.

In half the cases not prosecuted, U.S. attorneys said there was a “lack of evidence of criminal intent” or no evidence a federal crime had been committed.

Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., and Sen. Charles Grassley, R-Iowa, say they are troubled by both the high rate of declined prosecutions and the reasons prosecutors cite for not pursuing the cases.

The lawmakers asked Atty. Gen. John Ashcroft and FBI Director Robert Mueller in a letter Friday to explain why so many FBI terrorism referrals are not being prosecuted.

FBI spokesman Bill Carter said the exhaustive investigative effort to unravel the Sept. 11 plot may have contributed to the large number of international terrorism referrals that federal prosecutors chose not to pursue.

“Did we open cases that went down blind holes? Probably,” Carter said in an interview. “But I don’t have any direct knowledge of that.”

The Sept. 11 investigation caused the overall number of crimes referred for prosecution by the FBI to drop by 23 percent during the first three months after the attacks. But by the end of March, the number of FBI referrals had climbed back to pre-Sept. 11 levels.

Despite assertions by Ashcroft and Mueller that the FBI was focusing more on terrorism prevention, the records show that bank robberies, drug violations and bank frauds accounted for more than a third of all FBI referrals in the first six months after Sept. 11. That’s roughly the same level as in the previous five years.

Leahy and Grassley said in their letter that the FBI’s continuing focus on bank robberies, drug violations and bank fraud raises “troubling questions about whether the FBI and Department of Justice are devoting sufficient resources to counterterrorism efforts.”

“Director Mueller has to put more agents on the trail of al-Qaida and other terrorists and leave the Bonnie and Clyde investigations to local authorities,” Grassley said in a separate statement.