WASHINGTON (AP) _ The AFL-CIO today endorsed plans for a nationwide labor boycott of American Telephone & Telegraph Co. if its unions strike later this month, a strategy that could put labor in the unusual position of funneling millions of dollars to a non-union company.

The federation's governing council approved the plan at its spring meeting, acknowledging AT&T's competitors were non-union but promising nonetheless to switch long-distance carriers if asked to do so by the Communications Workers of America and the International Brotherhood of Electrical Workers.

''The AFL-CIO will be prepared to mobilize its resources to assist union workers at AT&T and to call for the fullest support possible from affiliated unions, state federations and local labor councils,'' the council said in its resolution.

In an accompanying statement the council said, ''Despite the fact that most of AT&T's competitors are non-union, the AFL-CIO believes picket lines - whether visible or invisible - are a crucial form of communication to inform union members and other consumers about unfair actions taken by an employer.''

Officials of the CWA and IBEW said that in the event of a strike and boycott they would urge labor organizations and union members who use AT&T to instead use non-union US Sprint Communications Co.

''One of the opportunities we have is the power to severely impact the enormous revenues generated by electronic services of the telecommunications industry,'' CWA President Morton Bahr said Monday in touching on the proposal during a speech to the CWA convention in Los Angeles.

Labor officials familiar with the plan said that if Bahr and IBEW President Jack Barry decided to launch a boycott the 14 million-member AFL-CIO would urge its affiliate unions and their members to switch to Sprint by using that company's local access numbers. That process would allow members to use Sprint without having to switch long-distance carriers permanently.

AFL-CIO officials said most if not all of its member unions use AT&T for long-distance service, with some of the larger unions paying the company about $1 million a month.

''It's hundreds of millions of dollars a year,'' said Ms. Zucker, who said she could not immediately provide a more specific estimate.

She acknowledged that a non-union company would benefit from such a boycott but said, ''We are prepared to do this if we have to win jobs with justice at AT&T. ... We don't want to promote Sprint. What we are promoting is the fact that unions can do this, that thi is one tool we can use at the bargaining table to achieve a fair contract.''

An AT&T spokeswoman said the company considered the proposal ''self- defeating '' because it would help AT&T's competitors and therefore possibly cost union members their jobs.

The presentation to the AFL-CIO executive council comes at a time when the unions are grumbling about AT&T's negotiating positions, primarily a company proposal to shift more health-care costs to workers.

The talks are in recess and due to resume Monday, three weeks before expiration of current contracts. It is the first time the two unions have negotiated jointly with AT&T. CWA struck the company in 1986 but AT&T was able to keep half of its manufacturing plants open because IBEW workers continued to work.