DALLAS (AP) _ Bell Atlantic Corp. and DSC Communications Corp. said Tuesday they partially settled a longstanding dispute with AT&T Corp. and its former equipment-making unit, Lucent Technologies Inc.

The companies settled accusations that AT&T was hampering Bell Atlantic's Caller ID system, a small part of a $3.5 billion federal lawsuit filed in February 1996.

The main part of the suit was Bell Atlantic and DSC's contention that AT&T, through Lucent, was stifling competition by building crucial telephone equipment to incompatible standards. Lucent is now an independent company, spun off from AT&T in September 1996.

The companies' dispute with Lucent remains unresolved and will go to trial March 4.

Details of the settlement were confidential, according to a release from DSC, a Plano, Texas-based maker of telecommunications equipment.

The suit said AT&T had hindered the Caller ID system by not releasing long distance numbers, making the feature less marketable. The dispute was settled through court-ordered mediation, said Bell Atlantic spokeswoman Joan Rasmussen.

``We're pleased we reached agreements with both parties and we're glad to avoid further judicial action on these matters which we've always believed were without merit,'' AT&T spokesman Marc Manly said.

A spokesman for DSC did not return a page Tuesday evening.

The rest of the suit concerns digital telephone switches, which connect numerous individual telephones and offer software options to callers.

Lucent makes a majority of the digital switches used in the United States, followed by Northern Telecom, a Canadian firm. In 1984, the lawsuit said, Bell Atlantic bought 400 of these special switches for more than $3 billion.

Philadelphia-based Bell Atlantic and DSC, which also makes switches, said AT&T ``disabled and sabotaged'' the switches so that no one but AT&T can connect with or make software changes to them.