Millions of tons of American grain, often billed by U.S. farmers as the best that money can buy, routinely goes to export markets laden with chaff, dirt, broken kernels and other unwanted junk -- all perfectly legal under federal inspection standards.

But now, plummeting export sales and complaints by foreign buyers about the quality of U.S. grain have touched off intense debate in agricultural circles and provoked calls for tightening the standards.

The issue is not whether the standards are being met. In most cases they are, according to the Federal Grain Inspection Service (FGIS). Rather, the debate is over the adequacy of the standards and whether they are hindering farm exports, which this year are expected to drop to $28 billion, the lowest since a 1981 high of $44 billion.

"We are not price-competitive, but another factor is the quality image. We fall a little bit short on cleanliness," said Tom Mick, an official of U.S. Wheat Associates, a farmer-sponsored export promotion group. "We consider quality a major trading issue."

Added Jim Guinn, a quality specialist with the American Soybean Association: "It is a very important issue in the long run to help us retain the markets we have and to have the chance to expand."

The federal standards, which have changed little since 1917, allow specified amounts of moisture, unusable broken kernels and foreign material in export grain. Many say the rules have not kept up with changes in harvest, storage and shipping technology that often exacerbate the quality problem.

Despite efforts by grain-exporting firms to delay changes in the standards, the Senate and House agriculture committees plan hearings to review the quality issue and consider toughening the regulations.

"The problems have been with us for a long time," said Sen. Mark Andrews (R-N.D.), who will chair Senate hearings that are to begin today. "If we are going to gain a reputation as quality suppliers, we have to clean up our act."

Andrews has introduced a bill that would bar the addition of dust, grain-related materials or nongrain materials to export commodities. He said he is considering penalties for violators that would "put them in the slammer for a year or two."

Rep. Cooper Evans (R-Iowa), leader of a House effort to tighten standards, added: "Our quality is less than many of our competitors. How you address it is one of the problems."

Many experts agree that the problem begins on the farm, with shoddy harvest and storage practices, and that it builds on the way to export terminals. But the current system also has led to frequent charges that the powerful multinational export companies compound the problem by adding extraneous material until the grain just barely meets the standards.

Rep. Neal Smith (D-Iowa), thwarted in several attempts to tighten the inspection standards, said his observations at U.S. ports have convinced him that export grain is sometimes adulterated.

"It ought to be illegal -- that's the point," Smith said. "The practice is hurting the reputation of our grain. The vast majority of the grain comes from the farm in good shape. The foreign material is added at the export point. The profits are huge for the companies -- we're talking about millions of dollars [additional] per shipload from this."

Another critic, Chuck Frazier of the National Farmers Organization, said: "Most of the damage I have been able to find stemmed from local elevators and export terminals. Everybody believes he has a chance to add a little foreign material and water, and believe me, they do it. It happens all along the chain. We don't have adequate standards. They are set and dictated by the big companies."

"Exporters are pushing as close as they can to the tolerances, but exporters don't produce the grain," said Joseph Halow, executive director of the North American Grain Export Association, which represents trading firms. "Farmers admit they are putting stuff into the grain. They acknowledge that they are part of the problem," he said.

Halow said an industry task force expects to endorse some changes in standards that FGIS Administrator Kenneth A. Gilles is to propose soon. Gilles said the changes are intended to better inform buyers about quality, but not to reduce foreign materials in grain.

"From a quality standpoint, I would support the idea of no foreign materials in the grain," Gilles said. "But if you said there could be no foreign material or moisture, who wants to pay the bill? It would mean more inspectors, more inspections."

Gilles said FGIS has been unable to document farmers' charges of intentional adulteration of grain by rural elevators or exporters.