Representatives of the recording industry said yesterday that they have developed a technique to make it harder to copy records, audio tapes and compact discs -- but the system would depend on consumers' buying specially modified equipment that would prevent copying.

The "copy-code" system works by encoding recordings with an inaudible signal, or notch. Every time a tape recorder equipped with a decoder picks up the signal, it stops recording, leaving 25-second intervals of silence scattered throughout the copy, according to Donald McCoy of the CBS Technology Center in Stamford, Conn., which developed the device.

"With interruptions of that sort it would effectively eliminate the value of any recording," McCoy said yesterday.

McCoy and Stanley M. Gortikov, president of the Recording Industry Association of America Inc., demonstrated the technique yesterday, using a Barbra Streisand record, at a hearing of the Senate Judiciary subcommittee on patents, copyrights and trademarks. The recording industry is seeking legislation that would impose royalty fees on records and recording devices. The royalty measure is opposed by manufacturers of blank tapes and tape recorders, as well as some retailers.

The issue is home taping -- the widespread practice of copying recordings from records, tapes, compact discs and radio. Representatives of the recording industry call home taping piracy that robs song writers and composers and recording artists of royalties.

Opponents of the royalty measure contend home taping is legal and a reasonable use by consumers of the recordings they have bought. What the recording industry is seeking, according to opponents on this issue, is an unfair tax on its products.

The copy-coding system is supposed to work hand-in-hand with the royalty system. "The purchaser who wants a recording just for his or her own personal use would buy an 'uncopiable' version -- one that is encoded with the notch, while a purchaser who wants to make multiple copies would buy a 'copiable version,' " said Gortikov. The "copiable version" would be priced to "include compensation for the copyright beneficiaries whose music is being taped," Gortikov said. A royalty also would be charged for recording equipment built without a decoder.

Gortikov conceded that it would take decades before enough equipment and recordings had been produced with the "copy-code" to make a difference in home taping. Even if encoded recordings became widespread, consumers with tape recorders unmodified by decoders would be able to copy encoded recordings.

McCoy said that design of the system is complete and its developers are working on the semiconductor chips that would be the heart of the system. He estimated the cost of the chips, produced in large volume, would be about $1 each. He also said CBS plans to license the encoder and the scanner on a royalty-free basis.

Several senators said the technological approach to the home recording issue looks promising. "I don't know that it's a total solution, but it's a major step in the right direction," said Sen. Howard M. Metzenbaum (D-Ohio).

"I remain unconvinced that a fee on audio tapes and records is appropriate," said Sen. Dennis DeConcini (D-Ariz.). "I congratulate the industry on coming forward with a solution that doesn't tax the consumer more."