The process of writing legislation has often been compared to sausage-making, but rarely is rotten meat actually present at a congressional hearing. Yet some is expected this afternoon at a House Agriculture Committee hearing “to review technologies in the meat industry.”

The hearing is in the cross hairs of activists opposed to the spiking of packaged red meats with carbon monoxide gas, which keeps cuts crimson no matter how old the meat. Unable to wrangle a place on the witness list, some plan to make their olfactory point in the hallway.

Meat producers are enthusiastic about carbon monoxide, which in small quantities poses no risk when consumed. By keeping meat red it boosts sales of aging but still edible cuts that would otherwise be tossed or discounted because of poor appearance — a waste the industry says costs it $1 billion a year.

Opponents — including Kalsec of Kalamazoo, Mich., which sells extracts that slow the browning of meats and has been badly hurt by the use of carbon monoxide — have petitioned the Food and Drug Administration and the Agriculture Department to ban the practice, or at least submit it to a full safety review.

They point to studies showing that consumers rely primarily on color to determine meat freshness — modern packaging makes it impossible to smell spoiled meat — and argue that the FDA was wrong in 2002 to classify the treatment as “generally recognized as safe.”

The European Union has banned the practice because it can “mask visual evidence of spoilage.”

“The use of carbon monoxide in meat packaging is clearly deceptive to consumers,” said Donna Rosenbaum, executive director of Safe Tables Our Priority, an advocacy group in Northbrook, Ill., created after four children died and hundreds became sick from eating tainted Jack in the Box hamburgers in 1992 and 1993.

On Oct. 22, her group and three others — the Consumer Federation of America, Food & Water Watch and the Government Accountability Project — sent a letter to Agriculture Committee Chairman Collin C. Peterson (D-Minn.) asking for a place at the hearing table, to no avail.

Peterson’s state is home to Precept Foods, a major player in carbon monoxide treatments. It is a joint venture between a subsidiary of Cargill Inc. and Hormel Foods Corp., both also of Minnesota.

A committee staff member said that the hearing is for those who develop and use new meat technologies and that “there will be other opportunities for the committee to hear from other stakeholders” at a later date.

In fact, Kalsec was invited to testify but declined, a company representative said, on the grounds that it did not want the hearing to morph from one about consumers’ “right to know” into a David-and-Goliath argument over money and market share.

“But that’s exactly what it is and has been from the start,” countered Randy Huffman of the American Meat Institute Foundation in Washington. The industry is “fed up” with the suggestion that consumers are being duped, he said, adding that the meat “has enjoyed enormous consumer acceptance.”

Huffman said new data to be presented today along with a letter of support signed by 17 “independent scientists” should help allay safety fears. But the industry has its work cut out for it.

Already, several supermarket chains, including Giant Food, Stop & Shop and Safeway, have announced they will no longer sell carbon-monoxide-gassed meats. And Tyson Foods, the nation’s largest processor of meat and poultry, recently said it would stop using the technology.

Those decisions came after the companies received five-page letters from Rep. John D. Dingell, chairman of the Energy and Commerce Committee, and Rep. Bart Stupak, chairman of the panel’s oversight and investigations subcommittee — Democrats from Kalsec’s home state of Michigan.

The letters asked how the companies are ensuring that consumers are not being fooled about freshness and demanded reams of data going back several years. Among other sensitive issues, the congressmen asked for data on how often the companies’ refrigerators get too warm and how much spoiled meat is returned by customers.

An Oct. 11 letter to Dingell and Stupak from a lawyer representing Giant and Stop & Shop showed the impact such letters can have. It informed the legislators that those stores had decided to drop the treated meat.

“Based on conversations I have had with . . . the Committee staff, it is my understanding that this decision by Stop & Shop/Giant addresses the concerns raised by your letter,” lawyer Theodore M. Hester said in the letter. “. . . And, accordingly, that it will not be necessary for Stop & Shop/Giant to provide the committee with the information requested by that letter.”