WASHINGTON (CNN) -- The nation's new gun check program is stopping the purchase of fewer firearms than expected, the FBI reports.

The National Instant Check System denied 3,348 gun sales out of 216,000 attempted purchases in its first two weeks, the FBI reported Monday. That is less than 2 percent of attempted firearms purchases processed by the FBI, officials said.

"That's 1.55 percent denials so far, and we were expecting about 2 percent," the system's program manager Jim Kessler told CNN.

But Kessler said an updated denial rate could approach 2 percent, because thousands of attempted purchases are in a 72-hour delay period. If a computer check prompts a question, the FBI has three days to determine the purchaser's qualifications.

Kessler says in many cases, states have been slow to determine whether someone with an arrest record was ever convicted, and gun sales cannot be denied based on arrests without convictions.

Except for early computer problems, the Instant Check program has performed satisfactorily, Kessler said.

Altogether, 372,565 background checks have been processed, but 42 percent of them were handled by 27 states which are not fully a part of the Instant Check System. The FBI has no figures on the number of gun sales denied by those states.

CNN Correspondent Terry Frieden contributed to this report.