Three members of Congress joined organizations for the elderly yesterday in denouncing a proposed amendment to the catastrophic-illness insurance bill for Medicare beneficiaries that would make it harder to obtain low-cost generic drugs.

Rep. Ron Wyden (D-Ore.) said the amendment would result in an increase of more than $100 million a year in the costs of the outpatient prescription drug program established by the bill without any medical advantage to recipients, because generics are generally as good as brand-name drugs. Reps. Fortney H. (Pete) Stark Jr. (D-Calif.) and Henry A. Waxman (D-Calif.) also criticized the amendment.

Rep. Andrew Jacobs Jr. (D-Ind.), who plans to introduce the amendment Wednesday, said he was asked to offer it initially by spokesmen for Eli Lilly & Co., a drug manufacturer in his home city of Indianapolis. He said the amendment would avoid "one more federal regulation which duplicates state regulations" on the same subject, substitution of generic drugs. Jacobs added, "The president of Eli Lilly contributed $1,000 to my opponent in the last election. I fully expect him to do it again."

But Jacob Clayman, president of the National Council of Senior Citizens, said, "There is absolutely no reason why this amendment should pass -- except to pad the pockets of the pharmaceutical industry with more money." The American Association of Retired Persons, Consumers Union, National Association of Retail Druggists, National Association of Chain Drug Stores and other groups also oppose the amendment.

Under the bill, Medicare would pay 80 percent of the costs of outpatient prescription drugs in excess of $500 a year per person. Included are financial inducements to druggists to substitute low-cost generics for higher-cost brand-name drugs unless the doctor, in his or her own handwriting, specifically writes on the prescription form that the named brand is medically necessary.

Jacobs' amendment would wipe out the requirement that the doctor certify that the named brand is medically necesssary, and would defer to state law on the form the doctor can use to mandate use of the named brand. Each state has its own rules. In some, a preprinted instruction appears on the form and the doctor need only check it off.

Waxman said use of state rules makes it easier to insist on brand-name drugs. The National Council of Senior Citizens said that in states using forms with checkoff boxes, only a third of the prescriptions are filled with generic drugs.

The Pharmaceutical Manufacturers Association said it favors the Jacobs amendment because having one set of federal rules for the Medicare program and separate state rules for general use could cause "confusion among doctors and pharmacists and could lead to unintentional switching."