Underlying the central third of Utah may be some of the nation's richest oil deposits, buried miles below the surface amid rock formations nature laid more than 700 million years ago.

But with their exploration interests captivated by overseas prospects, domestic petroleum companies are unlikely to be sinking new oil wells in the state anytime soon."It's a great academic find at this point, and a lot of the industry is aware of the potential," said Dave Allin, a Salt Lake consultant who advises several large oil companies.

"But as far as acquiring leases themselves and beginning the (development) process . . . it hasn't been greeted with a yawn, but there hasn't been a major rush," he added.

Allin said such companies as ARCO and Exxon are keeping abreast of studies on Utah's potential untapped oil fields, but major oil companies essentially abandoned domestic exploration in the early 1980s - and are unlikely to resume them in the near future.

Geologists believe oil-producing stone of the Late Precambrian age may be scattered throughout a roughly 300-by-100-mile band stretching from the Utah-Arizona border north into Wyoming.

"The exciting thing to us is that very few wells have been drilled in this older rock, so there's the possibility of sizeable oil deposits there that no one has discovered," said state geologist M. Lee Allison.

The state geologist's office, in cooperation with the U.S. Geological Survey, is in the second of an informal three-year study to determine just how rich Utah's Precambrian oil deposits may be.

Allison said the potential reserves can't compare to the 10 billion barrels Alaska's Prudhoe Bay Field is thought to hold, but it could be substantial, nonetheless.

"It could be hundreds of millions of barrels, but that's just pure speculation," Allison said. "We don't know the exact shape or size of the Precambrian distribution."

However, initial findings are promising. Using rock samples from wells and outcroppings in Utah, geologists have found "source rock" indicative of oil deposits in southern and central Utah, and possibly as far north as the Uinta Mountains.

Any Precambrian deposits that exist are almost entirely untouched. More than 9,500 oil wells have been drilled in Utah, but only 43 penetrated Precambrian rock levels - roughly 15,000 to 18,000 feet, Allison said.

He emphasized that what has been found is organically rich rock, not actual Precambrian oil deposits. What excites geologists is that the rock is averaging 3 percent total organic content, ranging to 10 or 11 percent in some places. Allison said 1 percent is generally considered enough to justify exploration. What's more, the kind of petroleum such formations create is "high-gravity, which means it's thinner, more like gasoline than tar, a very high quality oil."

Almost every major oil company is interested, if not rushing drilling rigs into such Precambrian target areas as southern Utah's Kane County or the Uintah Basin, some 200 miles to the northeast.

"We've had dozens and dozens of calls," Allison said. "But we haven't seen any real strong upsurge in drilling. The major oil companies would more likely go with shallower deposits. They are reluctant to go after something deep and speculative like this."

Oil production from existing wells in southern and eastern Utah has been on a steady decline for the past five years due to dwindling demand, says Jeff Burks, an analyst with the state's Energy Office.

The cost of a barrel of oil crashed in 1986 from $23 to $11 a barrel, and while Utah oil now is fetching $26 a barrel - up $7 from pre-Kuwait invasion prices - demand remains low in a still-glutted petroleum market.