The U.S. Postal Service will hand-deliver checks of $350 each to most of its heavily unionized 600,000 rank-and-file workers next month while the rest of the folks in the federal establishment are waiting to find out when or if Uncle Sam has any good news about raises for them.

The nation's mail movers (including most of the 17,424 postal aides in the Washington area) will get the $350 lump-sum checks, as they did last August and the summer before that, thanks to their union contract with the USPS.

That contract also calls for three pay raises of $300 a year, plus cost-of-living adjustments every six months. Counting all forms of payments--including a $500-per-worker payment when the contract was ratified in 1981--that amounts to 13 different increases in three years, one reason that eight of every 10 postal workers carry a union card.

By contrast, the government's 1.2 million white-collar workers and the 500,000 wage board (blue collar) employes cannot bargain over wages or fringe benefits. As a result they have not had a pay raise since last October and--barring a legislative miracle--they may not have another one until October 1984.

Senate-House conferees did approve a compromise budget for the upcoming fiscal year that provides for a 4 percent white-collar pay raise next January. But the full Senate and House must approve that compromise, and the White House has repeatedly indicated that the president doesn't want a federal pay raise until late in 1984.

That pay day could be a good one, since occupants of the White House tend to get generous with U.S. workers right before elections.

The promise of a dandy pre-election pay raise next year doesn't impress government employes who know that promises are not negotiable at supermarkets or real estate offices.

Potential pay raises don't impress most of the town's 300,000 white- collar feds when they hear about the union-label gains won by their postal colleagues, who got tired of being the low people on the government pay totem pole. If this sort of thing keeps up, the white-collar folks might get tired too!