After four of his friends died when a coal mined caved in 15 years ago, Pat Conkle gave up coal mining and set out to design a device to warn miners when mine roofs shifted.

Now that Conkle and his business partner, Ed Rozman, have produced the device, they contend that they are caught in a "bureaucratic, Catch-22 nightmare" featuring the federal government.

Put simply, the Labor Department's Mine Safety and Health Administration urges coal companies to install underground roof monitors voluntarily. But most coal mine operators don't want to do that, in part because they say such devices would expose them to more potential legal problems and damage claims.

The mine operators say that the liability problems could be overcome if the federal government required coal companies to use roof monitors. Nevertheless, they are opposed to any additional government safety regulations.

As a result, the United Mine Workers of America maintains, underground miners are not being protected as adquately as they could be. While the union doesn't endorse individual products, such as Conkle's, it says that it is convinced that roof monitors are effective and should be required by the federal government.

Each year, more underground miners are killed by roof collapses than any other type of mine accident. So far this year, 13 miners have died nationwide when roofs caved in, and 18 others have been seriously injured in 31 roof-related accidents in MSHA District 3, which includes Maryland and northern West Virginia.

Roof monitors are not a new idea. For years, miners have been trying to predict when a roof might fall, usually by keeping an eye on wooden support beams to see if any have cracked.

As mining became more sophisticated, several types of roof monitors were introduced, but few have received as much attention as Conkle's "Guardian Angel." When introduced in late 1978, the Guardian Angel was hailed by industry magazines, which said it was different from other monitors because it was simple to install, was reusable and cost only $27.

The Guardian Angel is inserted into a mine roof much like roof bolts are put into mine ceilings to help support them. The monitor can be set to indicate if a roof has sagged or shifted as little as 0.015 of an inch. If a roof moves, a red reflector pops down to warn miners.

Several coal mines in Colorado bought Guardian Angels in 1979 and 1980 after the Interior Department's Bureau of Mines tested them and concluded they were "a simple, accurate device for measuring and warning of roof sag."

Conkle and Rozman were about to sign a production contract in 1982 with the United Coal Co. of Bristol, Va., to market the monitors when demand for the devices plunged.

"The orders stopped, and we started hearing reports that the mines were pulling out our devices," Rozman said.

Richard A. Wolfe, a vice president of United Coal, said his company "has not given up on the concept," but hasn't signed a contract because of "legal concerns." Company lawyers, Wolfe said, warned that the firm might be held liable if a Guardian Angel failed to warn miners before a roof collapsed.

Coal company attorneys also said the business might be exposed to lawsuits for not installing enough monitors or for setting them to measure too large or too small a roof shift.

Rozman said that several coal company executives told him they would only install the devices if the MSHA established standards for them and required their use. But at the same time, the owners said they would oppose any attempt by the MSHA to toughen mine roof regulations.

A spokesman for the Bituminous Coal Operators' Association, which watches safety regulations for coal mine owners, would not comment on Conkle's device. But he said operators generally don't believe roof monitors devices are reliable.

The MSHA is in the midst of rewriting its roof regulations as part of an agency-wide regulatory review. But few observers believe the agency will require owners to install monitors.

Labor Undersecretary Ford B. Ford, who served as MSHA administrator in the first two years of the Reagan administration, has told members of Congress from coal-mining states that roof monitors "probably have merit" but are not practical.

For instance, Ford said, one section of a roof in an underground mine might sag up to one-fourth of an inch without falling while another section might collapse after dropping a fraction of that distance.

For monitors to be effective, Ford said, a mine owner would have "to establish a large-scale rock mechanics program to develop baseline criteria from which the safe roof movement for specific strata conditions could be established." The owner, he added, also would have to update that information continually.

But Rozman said, "They've created a Catch-22 situation. If you don't use any kind of monitor, then you don't have to make a decision and you can't make a wrong decision."