The United Mine Workers union is threatening to call a nationwide "job action" if the Reagan administration attempts to cut federal black lung benefits now paid to about 77,500 miners across the country.

"We will call for all coal miners in this nation, union and nonunion alike, to lay down their tools and walk away from the country's coal mines" if the administration attempts "to gut this most humane and necessary program," UMW President Sam Church Jr. said yesterday.Telegrams containing an identical warning were sent over the weekend to all members of Congress, a UMW spokesman said.

The UMW warning was prompted by a Labor department recommendation that benefits paid from the two-year-old Black Lung Disability Trust Fund be limited to those miners "who are truly medically disabled by black lung." The disease is a form of pneumoconiosis -- attributed to the inhalation of coal dust particles -- that affects breathing and often leads to death.

Payment restrictions are needed because the fund "rapidly is sinking into insolvency" and "producing massive deficits . . . financed from general revenues" from the U.S. Treasury that now amount to $956 million, the department said in its budget report. The department alleged that 88 percent of all the miners certified as eligible for black lung payments "were either not disabled or else could not be proved to have black lung disease."

Church agreed with the department's recommendation that the fund be made self-sustaining, largely supported by the coal companies. But, noting that 4,000 miners die annually from black lung disease, he vehemently disagreed that benefits should be curtailed through stricter eligibility requirements.

Church said his telegram was meant to "thank the many congressmen" who had helped the union in the past and to gain "their support in keeping the black lung program from being undercut."

He may have gotten that support from at least one cranny of the Hill.

For example, Labor Secretary Raymond J. Donovan journeyed to the Hill late Monday afternoon for a 40-minute "get-acquainted meeting" with Rep. Carl D. Perkins (D-Ky.), chairman of the House Education and Labor Committee and the legislative patron saint of the nation's coal miners. l