The Food and Drug Administration has barred government agencies from buying certain drugs from Abbott Laboratories, charging the company failed to correct violations of quality standards at a suburban Chicago plant. The FDA also said it would not approve any new drug applications by the North Chicago-based pharmaceutical giant that involve certain products made in the plant. In a letter to Abbott dated March 14 but not released until Tuesday, the FDA said some of the company's products are adulterated because of improper manufacturing practices. The agency's district director in Chicago, Raymond Mlecko, said FDA investigators did not find unsterile products at the plant, but did see violations of federal manufacturing requirements. The letter warned that the FDA was prepared to take more severe measures, including seizing products and shutting down manufacturing operations, if Abbott did not quickly correct the alleged problems. Donald Wright, Abbott's corporate vice president of quality assurance, said the FDA action resulted from a misunderstanding about the extent to which the firm has worked to correct the problems. Wright said the problems should be remedied soon and would have no material effect on Abbott. A health industry analyst, Michael Harshbarger of Chicago Corp., said the FDA letter had ominous implications. ``This is not a slap on the wrist,'' he said. An FDA report in November cited the Abbott plant for failure to maintain proper sterilty, failure to follow up on quality problems and in at least one case, making improper changes in records designed to show that a drug was made in an approved manner. The drugs involved are an antibiotic called erythrocin lactobionate and a batch of an anti-inflammatory steroid sold under the brand name A-MethaPred that is given to patients in hospitals to treat severe arthritis and lupus _ a chronic inflammation of the tissue around the joints. Mlecko said there was no evidence that the problems pose any immediate public health risk.