It ain’t over yet. At least, that’s what I heard from a pride of economists I called last week.

Investors in some of the most tightly wound tech stocks and dot-coms saw their lives pass before their eyes when prices plunged early this year. Some stocks have recovered, some haven’t.

But the Miracle Economy itself could still have years to run. Among the underlying strengths that remain in force: strong corporate investment, globalization, new technologies, more efficient capital markets and stellar productivity.

Much of the productivity gain comes from the companies that make and use computers, but the demographic trend is running in its favor, too.

“It’s the baby boomers,” says Mark Zandi, chief economist of RFA Dismal Sciences in Pennsylvania. “They’re now in their most productive years.”

In February, this expansion entered the record books as the longest ever. Consequently, you hear it referred to as “late cycle.”

But there’s no statistical connection between the age of an upswing and how much longer it can last. “Expansions don’t go through youth, middle age and then inevitably croak,” says Timothy Taylor, of the Journal of Economic Perspectives.

When they croak, it’s for a reason. Something comes along and shoots them down.

There’s a whiff of powder in the air. Growth and consumption are roaring, workers are in short supply, and the global expansion is putting pressure on commodity prices all worrisome things, says economist Barry Bosworth of the Brookings Institution in Washington, D.C.

Price inflation ran at 2.7 percent last year, up from 1.6 percent in 1998 still low but not a confidence builder.

To keep inflation from embedding itself, the Federal Reserve will keep raising interest rates, to slow the boom. As I hope you learned in Investing 101, the Fed always gets its way.

With luck, the economy will slow gradually, to a sustainable place. But there’s always a risk that the Fed will overshoot, producing a worse economy than planned.

The long boom has left investors feeling pretty safe about stocks. But although stocks in general do better than bonds or cash, individual stocks can suddenly plunge. Here are some thoughts about handling a stock portfolio now:

-High-techs and dot-coms. Are they a bubble? “You bet they are,” says economist John Makin of the American Enterprise Institute in Washington. The big question is whether the Fed can prick it without shedding more carnage all around.

Most vulnerable are the companies that have no current prospect of profit yet burn through cash. They have to raise money by issuing new stock. But with the Fed on the warpath, they’re less likely to find new investors.

-Cash and bonds. If you moved some money out of stocks, you’re probably glad you did. If not, and you’re playing with money you’ll need in a couple of years, take it off the table now. A good scare is always better than good advice for those who invest beyond their means.

-Stocks and stock-owning mutual funds. Long-term and aggressive short-term investors are prospecting for opportunities. There should be many of them, if the economy indeed behaves.

There are beaten-down stocks, such as real estate investment trusts, which should rise once the interest-rate hikes stop. There’s also a lot of interest in international and emerging-market mutual funds.

“Those countries are copying America’s miracle, with New Economies of their own,” says Allen Sinai, chief global economist for Primark Decision Economics in New York.

With global expansion still looking good, the case for global growth stocks remains good, too. But Taylor’s long-term favorite remains the U.S. market as a whole. He buys it through total-market index funds, such as those at Vanguard and Charles Schwab, which follow the Wilshire 5000 index of both larger and smaller stocks.

-Personal debt. Once interest rates start going up, no one can predict how high they’ll go, Sinai says. Don’t have debt you couldn’t carry if your interest cost rises by 1.5 percent.

The Fed is especially worried by the surge in “sub-prime” credit for people already heavily in debt (around 12 percent of households, by its latest count). Also, by the surge in margin debt money borrowed from brokers to buy stock. Margin debt shot up 25 percent from October to December last year.

In the past, Golden Ages have ended badly.

“It doesn’t pay to get too cocky,” Taylor says. You hope for the best, but don’t go too far out on a limb.

Syndicated columnist Jane Bryant Quinn can be reached in care of the Washington Post Writers Group, 1150 15th St., Washington D.C. 20071-9200.