Federal officials are investigating whether a subsidiary of RJR Nabisco Inc. falsely certified that tobacco in 160 million cigarettes exported to Japan met U.S. safety standards when in fact they contained up to five times the legal limit for one type of herbicide, government and company officials confirmed yesterday.

About 1.08 million tainted cigarettes already have been distributed in Japan through a sales promotion to retailers. A spokesman for R.J. Reynolds Tobacco USA, the company involved, said the cigarettes do not constitute a health hazard and said each retailer received only one pack. Reynolds has agreed to dispose of an additional 16,000 cases of cigarettes that were shipped to Japan earlier this year but not distributed. There are 10,000 cigarettes in a case.

In North Carolina, more than 350,000 pounds of Reynolds tobacco and 4,000 cases of cigarettes are being held under seizure orders by federal authorities. All are said to contain levels of the herbicide dicamba that exceed U.S. standards.

The U.S. attorney in Greensboro, N.C., and the U.S. Customs Service are conducting a criminal investigation into the import of the blended tobacco from Reynolds' West German subsidiary. The tobacco is believed to have originated in Pakistan.

Copies of cables that apparently were sent between the State Department and the U.S. Embassy in Japan provided details of the shipments and the investigation. One, from the State Department, says "RJR, perhaps knowingly, gave false certificates that the tobacco was tested and that it complied with legally permissable levels of chemical residues."

The cabled response from the embassy in Japan said Japan has no legal limit on dicamba in tobacco, so that the only possible legal violation would involve importation of the tobacco into the United States. But the cable went on to suggest that "sensitivities in Japan" could lead to a " 'health scare' that could spread to other U.S. cigarette manufacturers products."

The cable also said the Japanese Foreign Ministry had asked that federal prosecutors keep quiet about the export of the tobacco to Japan and concentrate only on its import to the United States, so that "the Japanese press would be less likely to learn of the incident."

The discovery of the contaminated tobacco comes at an awkward time for U.S. tobacco companies, which are seeking to vastly expand their market share in Japan because that country earlier this year lifted stiff import restrictions on American cigarettes. And it comes less than a year after the law went into effect requiring tobacco imported into the United States to adhere to the same herbicide-content standards as domestic tobacco.

State Department spokeswoman Laura Jehl confirmed that customs and "other authorities" are investigating shipment of the tainted tobacco, but would not confirm the authenticity of the cables. Robert Edmonds, U.S. attorney for the middle district of North Carolina, said he is conducting an investigation of RJR.

Reynolds spokesman David Fishel said from Winston-Salem, N.C., that the contamination of the tobacco was discovered by inspectors from the U.S. Department of Agriculture after the 16,000 cases of cigarettes -- Winston Lights -- had been shipped to Japan. Early testing had revealed no evidence of contamination, Fishel said.

"We put a hold on the product, stopped manufacturing here and notified the USDA we were going to make disposition of the tobacco based on their regulations," Fishel said. He said dicamba works by overstimulating plant growth, so that the roots can't support the plant and it dies.

It is prohibited on tobacco, he said, because it makes green leaves turn gold and thus appear ripe.

Reynolds is cooperating with the U.S. attorney and customs in their investigations, he said.

Karen Snyder, a research associate with the Natural Resources Defense Fund, said that research on the health effects of dicamba is relatively skimpy. The Environmental Protection Agency says the chemical itself appears to pose little toxic or environmental hazard, Snyder said. But, she added, the EPA notes that two chemicals that can contaminate dicamba during the manufacturing process -- dioxin and nitrosamines -- have been found to be carcinogenic.

Rep. Henry Waxman (D-Calif.), chairman of the health subcommittee of the House Energy and Commerce Committee, Friday asked Secretary of State George P. Shultz to provide all correspondence, memoranda and cables relevant to shipment of the tainted tobacco.

In his letter to Shultz, Waxman also charged that "these cigarettes were originally intended for the U.S. market and . . . a corporate decision was made to divert these products to the Japanese market."

Fishel, the Reyolds spokesman, denied the allegation, saying that particular blend of tobacco was made to suit Japanese tastes and was intended entirely for export.