Thirty-seven days from the time when they either must sign a multi-million dollar contract or lead a multimillion dollar strike, the chiefs of the nation's postal unions are warning the White House to back away from bargaining talks with postal managers.

On July 20, the three-year agreement between the U.S. Postal Service and its half million union workers expires. Although both sides are down-playing strike talk, the USPS (as reported here) has alerted the Pentagon that it may need federal troops to help sort, guard and deliver the mail if workers strike - as they did in 1970.

Unions involved in the negotiations have their own strike contingency plans, and token funds that would beused to help tide over members during a walkout.

Leaders of the three main AFL-CIO unions, which represent clerks, mail handlers, letter carriers and most other crafts, told reporters yesterday that the nonwage bargaining is not going as smoothly as USPS officials say it is.

The union presidents - from the American Postal Workers Union, Letters Carriers, and Mail Handlers - say "irresponsible" White House attempts to "jawbone" them into holding wage demands around 5.5 per cent have made tougher for both sides to bargain. After the meeting, one of the union officials told a reporter that the White House had created a political situation within the 500,000-member unions that has made employes bitter and resentful and more likely to strike if they don't get a "good" package.

The unions will make their first wage demand next Monday. It probably will be in excess of 15 per cent, about tripple in the amount the White House has laid down for nonpostal federal pay raises this year.

By law, the White House and Congress are excluded from postal labor negotitations. Administration officials have made it clear that they are keeping an eye on the contract, which will be the biggest, and perhaps most costly of 1978.

To strengthen the unions' position the AFL-CIOs public Employes Department today is expected to endorse a statement telling the White House to keep out of the bargaining, demanding that the USPS retain the "no layoff" pledge in any new contract, and urging Congress to quickly approve a union-backed postal reform bill that would increase subsidies to the Postal Service.

APWU President Emmet Andrews said the postal reform bill is necessary to allow the service to continue operations, and to bury the "mission impossible myth" of a pay-as-you-go Postal Service financed with frequent rate increases.

J. Joseph Vacca of the letter carriers union said his members are upset because of speedups in the postal Service resulting from elimination of thousands of jobs by attrition at a time when workload is increasing.

Lonnie Johnson of the mailhandlers union said he was unhappy with White House interference in the bargaining talks, and is getting the impression the White House is antilabor.

Jim LaPents, chief negotiator for the three unions, said management has come to the bargaining table with bad attitude, brushing off contract violations at the local level, and insisting that no changes are necessary to correct them.

Andrew said the savings the USPS has made by eliminating 40,000 jobs through attrition has been more than offset by mandatory overtime that, he said, is costing the service nearly $800 million a year.

The union leaders said they hopped a contract can be tentativley approved (a mail referendum of members is necessary to retify it) by July 20. But they said they will stand together if a strike becomes necessary.

In 1970 an estimated 220,000 postal workers went out on a wildcat strike that lasted 10 days. It was ended when President Nixon ordered U.S. troops into some post offices and guaranteed the workers a 14 per cent raise.

Postal workers now average about $15,000 a year, thanks to their present contract that gave them three regular raises, and six cost-of-living raises, which increased salaries nearly $3,000 in three years.

This time union say, they want two-year agreement that will provide for substantial pay increases, continuation of cost-of-living boosts and an end to job cutbacks by attrition.