Southern congressmen poised to lambaste R.J. Reynolds Tobacco Co. for sending pesticide-tainted cigarettes to Japan learned yesterday that the disputed chemical is regularly used by some American tobacco growers.

The House tobacco and peanut subcommittee hearing, at which Chairman Charlie Rose (D-N.C.) took the unusual step of putting witnesses under oath, was spurred by a controversy over Reynolds' shipment of cigarettes tainted with a chemical called dicamba to Japan earlier this year.

Rose and tobacco-state allies came prepared to attack Reynolds for smearing U.S. tobacco growers in order to protect its reputation, but testimony from Agriculture Department officials and executives from chemical companies and the cigarette firms indicated that dicamba is widely used on tobacco in this country.

Even so, Rose said that he and other tobacco-state representatives were incensed that R.J. Reynolds was blaming the trade embarrassment on U.S. growers' use of dicamba, which is not authorized by the government for tobacco.

"We can't understand why R.J. Reynolds would come up here and ask for our help on excise taxes and other things and then stretch so far to blame our growers," Rose said.

The chemical has been used widely as a broadleaf weedkiller on food crops in this country for 20 years, with laboratory tests exonerating it of any adverse health effects. But because tobacco is a broadleaf plant, growers generally do not use dicamba on it for weed control.

They have discovered, however, that lightly applied dicamba acts as a ripening agent that hastens the tobacco leaf's change to a golden color. Reynolds argued that since the chemical is harmless, it ought to be allowed for use on tobacco. But Rose and others contend that it results in a leaf that does not meet quality standards and would put U.S. leaf at a disadvantage to foreign tobacco.

Agriculture Department witnesses yesterday indicated that routine testing had turned up dicamba residues on a small percentage of tobacco marketed through the federal crop support program. In three cases where residues were found, farmers' support payments were ordered withheld.

But that did not lessen the tensions between Reynolds and the subcommittee, which hinted that the company was attempting to undermine American farmers in order to promote cheaper foreign tobacco.

Reynolds senior executive vice president Robert J. Carbonell contended that the firm had traced the dicamba to an American leaf that went into a blend of tobaccos from 11 countries prepared for a new line of Winstons that the firm had developed for the Japanese market.

But Rose and other panelists members expressed doubts about Reynolds' ability to trace the tainted leaf that precisely and elicited testimony from Agriculture Department witnesses that such detection is next to impossible.

The blending was done by a Reynolds affiliate in West Germany, and the tobacco was then sent back to North Carolina to be made into cigarettes for export to Japan. After USDA inspectors found dicamba on one shipment of the imported blend, Reynolds halted cigarette production.

About 16,000 cases of cigarettes that already had been shipped to Japan were embargoed by Reynolds, and replacement cigarettes, using a different blend, were sent.