The National Zoo's application for reaccreditation was put on hold yesterday amid controversy over a recent spate of animal deaths, forcing the world-renowned institution to make improvements and wait at least six months before it can reapply for full accreditation.

An accreditation commission for the American Zoo and Aquarium Association, meeting in Columbia, S.C., refused to grant the zoo the five-year accreditation normally given to zoos that are found to be operating smoothly. Instead, the commission gave the zoo a year to fix certain problems that it found -- but did not make public -- in the zoo's operations.

The zoo's Conservation and Research Center in Front Royal, Va., did receive accreditation for the next five years.

"The American Zoo and Aquarium Association tabled the National Zoo's accreditation, which means that we remain accredited for the next year while we address the AZA's recommendations," zoo spokesman Robert Hoage said last night. "The AZA commended us on the steps we've already taken and that we are continuing to take to ensure that the National Zoo maintains the highest standards in animal care." Hoage declined to comment further.

The action by the zoo association, a trade organization, is a severe blow to the reputation of the National Zoo and its director, Lucy H. Spelman, the zoo's former chief veterinarian. It was the first review of the zoo since Spelman became the director in June 2000 and the first time since accreditations became mandatory in 1985 that the zoo's application has not been granted on schedule.

The accreditation commission, as is its custom, did not release copies of its report and recommendations, which were given to the zoo and the Smithsonian Institution, which oversees it. Zoo officials also declined to make the report public yesterday.

A zoo employee familiar with the association's review said that, among other problems, inspectors spotted evidence of continued rodent problems at the zoo during a scheduled visit in January and found serious morale problems at the zoo's facility in Front Royal, where the Smithsonian had initiated and then dropped a plan to close the 3,200-acre facility.

Controversy about zoo operations erupted in mid-January when two red pandas were found dead after eating rat poison that was buried in their yard by a pest control contractor. Since then, there have been concerns raised about other animal deaths, including two zebras that died of hypothermia in the winter of 2000 when they weren't given enough to eat.

A House oversight committee conducted a hearing this month on Smithsonian operations, including questionable animal deaths at the zoo. The panel has asked the National Academy of Sciences to investigate and evaluate zoo management, including animal deaths in the past decade at the zoo and its Front Royal facility. A spokesman for the academy said yesterday that the $450,000 study would begin in April and take a year, with an interim report issued in six months.

The zoo receives more than half of its budget from federal funds.

Zoo officials have acknowledged that human error killed the red pandas and zebras and said they have taken steps to prevent a recurrence of the problems. But documents and interviews with zoo staff indicate that human error has been a factor in the deaths of at least six other animals.

Accreditation is vital for prestige, fund-raising and the ability to acquire animals or trade species a zoo no longer wants. Only a handful of zoos have their accreditation applications tabled each year, according to association spokeswoman Jane Ballentine.

Other big zoos whose accreditation has been tabled in the past decade include facilities in Dallas, Kansas City and Los Angeles. All regained accreditation within a year.

The National Zoo's first opportunity to renew its accreditation will be in September, when the zoo association holds its annual meeting in Columbus, Ohio. Otherwise, it must wait a year.

"Generally when [an application] is tabled, it is because the commission feels there are issues that need to be addressed but they can be addressed within a year," Ballentine said.

Tabling an accreditation application is a step that falls midway between denying accreditation and granting it. In evaluating zoos, the association is supposed to take a broad look at animal management and care, physical facilities, conservation and education programs, record-keeping, financial health and safety procedures.

The commission's inspection team made a prearranged visit to the zoo Jan. 29-31, shortly after the red pandas were found dead.

Yesterday's meeting of National Zoo officials and the accreditation commission was scheduled for early afternoon but was postponed until late afternoon after three officials flying to Columbia to join Spelman were delayed at Reagan National Airport, Ballentine said. The three were Smithsonian Undersecretary for Science David L. Evans; Clint Fields, president of Friends of the National Zoo; and William Xanten, the zoo's acting general curator for animal programs.

Staff writer James V. Grimaldi contributed to this report.