"You'd be surprised at the people who come in to exchange needles," said Larry Hilton, the executive director of AIDS/H.

Many of these 5,000 might be protected if they could exchange used needles and syringes for sterile ones.

The participants must show their cards to exchange needles and to establish that they possess the needles legally.

He said he had been exchanging needles for himself and a dozen other friends since last winter.

Currently, Dr. Desjarlais said, it is illegal to spend Federal money to evaluate programs in which addicts may exchange used needles for new ones.

But Donald Grove, an advocate for needle exchange programs, said, "They are not coming to the Lower East Side to exchange needles.

The cards are needed to exchange needles and establish that the participants possess them legally.

The storefront, with its tables laden with AIDS literature, was full of people, mostly young, exchanging needles.

But exchanging clean needles for used ones is more effective, it said, because as time passes fewer drug users follow the proper disinfection procedures.

Mrs. Whitman said she remained opposed to allowing addicts to exchange dirty needles for clean ones.