The Food and Drug Administration yesterday placed its stamp of approval on a controversial list of about 2,000 generic, inexpensive drugs equal in strength and quality to more expensive brand-name products.

"Now the sole remaining difference between drugs is the price," said William Haddad, who heads the investigative arm of the New York legislature and who headed the group that prepared the list.

According to FDA Commissioner Donald Kennedy, who announced the approval of the list during an appearance yesterday on the "Today Show" (NBC, WRC), any of the generic drugs on the list - drugs sold by their chemical name - may safely be substituted for their brand-name equivalents, which in some cases cost 500 percent more.

Following Kennedy's television appearance, the FDA released a statement in which it explained that it has endorsed the list as accurate, but has no intention of reproducing it or distributing it. "That's not our business," a spokesman said.

The Pharmaceutical Manufacturers' Association, which represents the major drug manufacturers and has long opposed laws requiring that consumers be provided with the least expensive drug available, yesterday attacked Kennedy's action.

"I say you can't make a statement that they are the same merely because they are on their list," said PMA President C. Joseph Stetler, who questioned whether all the generic drugs are produced by approved manufactures and asked whether all the drugs have been tested for equivalency.

"It's our policy that drugs which have the same active ingredients and the same dosage form and strenth and are generally known as being chemically equivalent are also therapeutically equivalent unless there's scientific evidence to the contrary," said FDA spokesman Wayne Pines.

"We regularly inspect all plants where drugs are manufactured," he said. "We have in this country a single standard for the manufacture of drugs."

According to Pines, there have been few examples of what is called[WORD ILLEGIBLE] two chemically similar drugs having different therapeutic effect - brought to FDA's attention. When such examples have been found he said, they have not always involved generic and brand-name drugs, but have also involved different batches of the same brand-name product.

One of the more strikingexamples of price differential in the New York State list is Chlordiazepoxide HCI - a tranquillizer known to million of Americans by its brand name, Librium.

The New York compendium lists 15 brand-name products, all said to be equal.

According to Haddad, a Long Island company buys 500 capsules of the tranquillizer from Barr Labs, a generic manufacturer, for $3.40, and sells them to drugstores for $4.85. Barr makes the same product for Lederie, one of the major brand-name manufacturers, said Haddad, and Lederie wholesales the capsules for $17.01 for 500.

Thirty-two states, the District of Columbia and Puerto Roco have laws allowing druggists to give a patient a generic product, rather than the brand name when the generic is available.

Only five states, however, including New York - where the law goes into effect in April - require the druggist to provide the less expensive product.

One of the arguments made in favor of the generic products is that many are manufactured by the brand-name manufacturers.