(Adds statement from families, paragraphs 4-7)

HUNTINGTON, Utah, Aug 19 (Reuters) - Hope is fading for six men trapped for nearly two weeks in a collapsed Utah coal mine after a fourth drill hole failed to locate them, a mine company official said on Sunday.

"It's possible they may not be found," Rob Moore, vice president of mine co-owner Murray Energy, told a news conference, expressing pessimism about the miners' fate for the first time.

The six miners have not been heard from since the Crandall Canyon Mine collapsed on Aug. 6. An effort to tunnel to them was halted after three rescuers were killed in a cave-in on Thursday.

The miners' families expressed frustration with mine and federal officials over the way the rescue effort has been handled.

"We feel that they've given up and are waiting for the six miners to expire," said Sonny Olsen, a spokesman for the families who read a prepared statement as about 60 relatives of the trapped miners stood behind him.

Olsen said the families had asked from the beginning that rescuers drill a 36-inch hole -- large enough for an escape capsule to be lowered into the mine -- but officials had "skirted the issue."

The four holes drilled so far have been about 9 inches in diameter or less.

A fifth hole -- also about 9 inches -- was started on Sunday but will take at least 58 hours to drill the 2,039 feet (621 meters) to the mine, Moore said.

Moore did not hold out much hope that the fifth attempt to find the missing miners would be any more successful than previous attempts or that, if they have already died, their bodies would ever be found.

"It's likely we'll see similar results there. We can't say that with certainty," Moore told reporters.

A microphone and video camera dropped over 1,600 feet (488 meters) into the fourth drill hole over the weekend did not detect any signs of life and found low oxygen levels in the mine.

"The results of the fourth bore hole are disappointing," Moore said. "Obviously, the air readings there do not suggest that they are sufficient to support life."

Richard Stickler, head of the U.S. Mine Safety and Health Administration, told the news conference that a crew of mining experts would evaluate the feasibility of again attempting to have rescuers go underground.

Stickler said the mountain where the six men were trapped "continues to be active, continues to move."

The three rescuers were killed when pressure from the mountain above caused rock and coal to explode from the walls of the mine.

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