NEW YORK (AP) _ Several show-business unions rallied Monday outside NBC headquarters to support a broadcast employees' strike against the network and a threatened directors' strike.

While the rally was originally organized to show support for the striking National Association of Broadcast Employees and Technicians, developments in the labor dispute between the Directors Guild of America and movie and television producers also received top billing.

''NABET and the other unions are faced with a conspiracy among ABC, CBS and NBC to destroy the rights of unionized workers,'' said Alan Gordon, an official in the directors guild. ''Today we're here to support NABET and to show them, notwithstanding our own problems, we can turn out members to help them.''

About 200 people attended the lunchtime rally in Rockefeller Center. Among the other unions represented were the Writers Guild of America, the Screen Actors Guild, the Union for the Performing Arts and the American Federation of Television and Radio Artists.

The directors have threatened to go on strike Tuesday morning against NBC, Warner Bros. and Columbia Pictures. The Alliance of Motion Picture and Television Producers has vowed to lock out all guild members.

''The Director's Guild is prepared to meet that threat (of a lockout). We will engage in a strike for however long it takes to make sure that NBC does not destroy the rights of our members,'' Gordon said.

NABET spokesman Arthur Kent thanked the other unions for their support.

''The three networks have shown the way they stick together, there is no reason why we can't stick together,'' he said. ''It is our salvation.''

NABET members, representing 2,800 workers in six cities, struck the network June 29 when NBC implemented new contract terms that included relaxed rules about hiring temporary employees. The union contends temporary employees would erode job security.

The first bargaining session since the strike began is scheduled for July 20. It will be moderated by a federal mediator.