The executive board of the American Postal Workers Union has decided to try to put a sister and rival AFL-CIO union out of business. The upcoming fight with the Mail Handlers Division of the very tough Laborers International Union could provoke a civil war in the house of labor just as contract negotiations with the U.S. Postal Service begin. The Postal Service is promising to play economic hardball at the bargaining table.

At stake are the hearts, and dues money, of about 38,000 mail handlers. Those employes, centered primarily at big mail-moving factories, will be asked to join the APWU, which represents mostly clerical types.

APWU will fight charges that it is raiding a fellow AFL-CIO union by pointing out that it already represents about 8,000 mail handlers in the big, militant New York region.

With 270,000 members, the APWU is nine times larger than the mail handlers union. But the smaller group has the backing and cloud of the Laborers International (560,000 members). The laborers president, like the head of the APWU, is a major figure in the AFL-CIO. That body's executive council will decide whether the organizing raid can take place.

Reached in Washington, James L. LaPenta, whe heads the public service division of the Mail Handlers, said the APWU plan is "a lot of wind and noise to make their members think they are doing something." LaPenta, a rugged negotiator who sometimes jogs from Virginia to his job downtown, said, "If they try to organize us we will whip their ass. Let me repeat that. We will whip their ass."

LaPenta said members of the predominantly black mail handler union would reject APWU because the union has tried "to take mail handler jobs for clerks through the arbitration process." He also said the APWU and predecessor unions had segregated locals in some southern cities until the early 1960s.

Whether the organization attempt is a serious move as the APWU contends or a leaky hot air ballon as the Mail Handlers see it isn't likely to improve relations between the leaders of the major postal unions. Although they frequently find themselves on the same side, insiders know there is little love lost between some postal union leaders who privately describe each other as "wimps," "blowhards,' or "moral cowards.

Returning to earth, the 2,000-plus delegates here are slowly plowing through 821 resolutions their members sent them to push, or oppose, here. Resolutions range from the serious -- the right to strike, presidential endorsement, laying out "must" items for the next contract -- to those less related to traditonal bread-and-butter unionism. The Iowa delegation, for example, wants the union to provide special pre- and post-divorce services to union members.

The giant Maryland-Virginia-West Virginia-D.C. delegation plans to cast all its votes, on every issue, as a unit, according to delegation leader Walter Kennedy. He said major items local members want resolved at this convention include more official time and protection for union stewards to handle grievances and protect members from harassment.

Roosevelt Odom, executive vice president of the D.C. local, said amnesty for workers fired last year during a wildcat strike is a "hot" item with his delegation. Several resolutions -- if approved -- would bar this, the biggest of all postal unions, from signing any contract with the Postal Service until the dozen or so fired workers are granted amnesty and restored to their jobs.

The D.C.-Maryland delegation wants a $5 per member per month assessment to bankroll a "contingency fund" in case the union strikes the Postal Service. Although strikes against the government are illegal -- the penalty is a year and a day in jail or a $1,000 fine or dismissal or all three -- there have been major and minor strikes in recent years by postal workers.

Compared with other federal workers, postal employes have an excellent work contract. Postal workers are highly unionized eight of every 10 are members -- and they bargain directly with the U.S. Postal Service on pay and working conditions. The price of postage stamps is tied directly to the contract package, since 80 cents of every $1 the Postal Service makes goes for personnel costs.

The present three-year postal contract expires in mid-July. Negotiations begin this April for a new agreement to continue annual pay raises, full cost-of-living adjustments every six months, and a continuation of the no-layoff promise.