On the theory that nothing in the stock market goes up forever, cautionary words on those torrid energy shares are increasingly popping up amid a recent 10% slide in oil prices.

The latest SOS I’ve come across is from a British worry-wart, London-based investment manager Stahler Dearborn, Ltd. About six weeks ago, roughly 18% of the firm’s American equity holdings was stashed in the energy sector. No more, though. The figure has been scaled back to just under 10%.

“I may be premature in cutting back, but I’m seeing more and more worrisome signs,” says Raymond Stahler, one of firm’s principals. Among them:

• Falling oil prices (from the high to the low $70s), and 5% in the past week alone.

• Increasing weakness in a number of the top-rated energy stocks, which suggests to Mr. Stahler a lower portfolio weighting is called for at this juncture.

• World-wide economic growth is slowing, which should temper demand. Likewise, demand from such hot economies as China and India should begin to taper off at some point.

• Near term, at least, supply seems to have caught up with demand.

• Technically, some big oil stocks look like they’ve broken down, and some technicians are projecting a near-term drop in the price of crude to the low to mid $60s.

• Increased analyst warnings on various energy companies.

• Given the recent Israel-Lebanon peace truce, oil could lose some of its terror premium (which some experts estimate at between $12 and $15 a barrel).

By the same token, Mr. Stahler says he recognizes that at any given point, considering the volatile situation in the Middle East, an event could occur — such as a conflict with Iran over its nuclear enrichment ambitions — that might suddenly push up the price of oil to between $10 and $20 a barrel. But for now, he points out, given the weakness in energy stocks, “you can’t rely on a wild card to bail you out.”

His concerns raise an obvious question: Is the blistering three-year run in energy stocks nearing an end? In this period, the median energy stock in S&P Index of small, medium and large companies has more than tripled, in the process generating an annualized return of nearly 45%.

Such a run is invariably a sign of caution for new stock purchases, but veteran investment advisor Richard Moroney thinks otherwise when it comes to energy shares. “The energy sector is not tapped out and statistics tell a bullish story,” he says.

He notes, for example, that despite the share price gains, the median energy stock trades at only 16 times trailing 12-month earnings, which represents a 20% discount from a year ago. How is that possible? Because during the past three years, the average energy company saw per-share profits rise at an annualized rate of 72%, even faster than share prices increased.

He further points out that the average energy stock trades at a reasonable 11 times the consensus 2007 profit estimate; likewise, despite a doubling in capital spending the past three years, the sector’s return on investment has risen in ten of the last 12 quarters.

As investors know, high energy prices have resulted in strong earnings and cash flows for energy companies, which have plowed the money into development projects (as evident by a 41% jump in capital spending in a recent 12-month period). Mr. Moroney, who is also the editor of Dow Theory Forecasts, a well-regarded monthly investment newsletter in Hammond, Ind., figures this capital spending trend bodes well for producers of equipment and services for energy producers.

In this vein, he notes oil services companies like Nabors Industries and Oceaneering International should continue to achieve outsized earnings gains as long as energy prices remain high relative to historical levels. Other favored energy stocks include Conoco Phillips, Chevron Corp. and Valero Energy.

The veteran money manager say he doesn’t see much of a break in energy prices, given growing worldwide demand and scarcity of product. “We’re talking about a commodity and so the price could always drop,” he adds. “But any fall is sure to be limited because the long term trend remains positive.”

Another significant plus for the sector, as he sees it: Stock valuations are still pretty low, based on multiples of cash flow and earnings. His top energy picks are EnCana Corp., Conoco Phillips, Chicago Bridge & Iron N.V., Nabors Industries, and Noble Corp.

His parting words: “The bull run in energy is far from over.”