(FORTUNE Magazine) - In 2000 it was the Federal Reserve's rate hikes that finally burst the dot-com bubble. Six years later, history may be repeating itself, this time in commodities.

Seeking to keep inflation in check, the Fed has raised short-term interest rates 16 times since 2004. Normally that would wreak havoc with commodity markets, since higher borrowing costs are a brake on economic growth, and commodities demand ebbs and flows with the economy.

This year, though, with commodities in vogue and demand still surging from India and China, the market has seemed almost immune to higher rates.

Until now, that is. The turning point seemed to be a troublesome report on April inflation - the consumer price index rose 0.6 percent, ahead of expectations. That disabused investors of the notion the Fed was nearly done tightening. Over the past few weeks oil fell from $75 to $70 a barrel; gold went down from $725 to $632 an ounce; and copper slid from $4.13 to $3.44 a pound.

A.G. Edwards commodities analyst Bill O'Grady thinks this dip is long overdue.

"The whole root of this bull market takes you back to 2001, when the Federal Reserve and the central banks in Europe and Japan cut rates in order to protect the economy from a significant decline," O'Grady says. "Thus it would make sense that as that liquidity is drained, prices would fall."

Just as technophiles insisted "This time it's different" six years ago, commodities bulls have a similar rallying cry today. Their "new paradigm" hinges on China.

But as O'Grady points out, China's economy can't keep growing at a 10 percent annual clip if credit-crunched U.S. consumers stop buying so many Chinese goods. Moreover, the bull case for China assumes a near-seamless transition from an agricultural to an industrial economy.

"When Stalin industrialized the Soviet Union, 13 million people died," says O'Grady. "To think that China is going to go through this industrialization without a hitch is just naive."

We're not saying that gold is going back to $300 or copper to $1. We're not even sure that their run is over. There were pundits warning of a dot-com bubble in 1998, remember, and it was another two years before the market finally crashed. What we are saying is that now is not the time to plow a lot of money into commodities.

What about commodities-related stocks that FORTUNE has recommended recently? We like Archer Daniels Midland (Research), the agricultural giant-turned-ethanol play, though not as much at $39 a share as we did when we first cited it in December at $23. The economic and political case for ethanol is still intact.

On the other hand, ADM is a little pricey now, at least compared with Bunge (Research), another agriculture company with ethanol exposure. Bunge, at $54, trades at 13 times earnings, vs. 23 times for ADM.

Copper miner Phelps Dodge (Research) seems a little riskier. We picked it at $72 (split adjusted) in December, and it got as high as $99 in May. Now at $76, the stock has its merits, including a hefty dividend yield (6.2 percent, including special payouts that are continuing), a modest price/earnings ratio (10), and a cautious management team that's hedging against lower copper prices. Still, we worry about what a sharp drop in copper prices might do to Phelps stock.

"We've had a combination of financial speculators driving up copper, which in turn has incited end users to hoard," says Ed Yardeni, chief investment strategist at Oak Associates. "That's not sustainable."

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There's still zip left in energy stocks