Julius Caesar received a significant and prophetic warning in February of 44 BC: Beware the Ides of March! Unfortunately, he ignored the warning and on March 15 of that year he was murdered.

On Wall Street, another warning of significant proportions is making the rounds: Beware the ides of September! In brief, some pros are saying, brace yourself; we’re in September, traditionally the worst month of the year for the stock market, and this period could get ugly, bloodying many investors.

The figures from Standard & Poor’s tell the sad story. Since 2000, September, largely reflecting the effects of the unraveling of the Internet bubble early in the century, has skidded an average 4.53% a year. Over the long run, though, the pain has been considerably less, with the S&P 500 averaging a September loss of only about 1% since 1970. Still, some pros argue that this September could be beastly, given a bevy of danger signs, most of which are expected to linger for the balance of the year and place ongoing pressure on stocks in 2007. Chief among them, they say:

• A major slowdown in the housing market — a number of pros are already calling it a bust — that some believe could well precipitate a recession.

• A slowing economy worldwide, plus repeated guidance from one company after another that slower times lie ahead.

• Recent hints from some Fed governors that interest rate increases, despite last month’s pause, may not, as many think, be over.

• High oil prices, which are increasingly being passed on to the consumer and pose inflationary implications.

• The likelihood of a rash of earnings downgrades from analysts because most profit estimates are widely believed to be too high.

• Mounting geopolitical dangers, especially as they relate to Iran and North Korea. Political speculation is widespread that either America or Israel will take military action before year’s end to wipe out Iran’s nuclear capabilities.

• The possibility that Wall Street could lose a pro-business Congress in the midterm elections.

“There’s enough in the worry pot to make you vomit,” says Los Angeles day trader Arnold Silver. “You have to be off your rocker not to be cautious and take some money off the table in this kind of market.”

A couple of Wall Street veterans echo such thinking. One, the president of New York’s Balestra Capital, James Melcher, believes investors face a poor market ahead — namely a down year in 2006 and a worse decline in 2007.

Mr. Melcher, who manages more than $200 million of assets, notes when the market was going up, “we enjoyed a positive re-enforcement cycle — a housing boom, good auto sales, a growing economy and short-term interest rates of 1%.” But now, he says, “we’ve moved into a negative re-enforcement cycle, with housing turning down faster than expected and rates having risen appreciably.”

The housing decline, he adds, will affect jobs, consumer expenditures and consumption, leading, he predicts, to a sharply slowing economy, abetted by record consumer debt. Some financial experts expect the housing slump to knock down the GDP by about 1%, but Mr. Melcher thinks its impact will be a lot worse.

As he sees it, because of the broad economic downturn globally, especially in America, “stocks do not make sense anywhere in the world, including the emerging markets.” He also holds the same near term view of commodities, such as energy, that he likes for the longer term.

Currently, his firm is marginally short (a bet stock prices will fall) and is holding a lot of cash. His favorite shorts, even though many have already fallen a lot, are shares of automotive and housing companies and mortgage lenders. Balestra Capital is also heavily short B-rated high yield or junk bonds, which Mr. Melcher believes are “way overpriced and should drop substantially.”

So where do you put money? Short-term Treasuries with a 5% coupon look pretty attractive, he says.

The words from our other bear, investment advisor Charles Allmon, who sees major geopolitical risks, are ominous. His big concern: The turmoil in the Middle East. “The fighting there will expand and who knows who else will get into the act?” he asks. “Sooner or later, I think, it’s going to affect the whole world and no one knows the next stop.”

The editor of the Growth Stock Outlook, a monthly investment newsletter in Chevy Chase, Maryland, contends “the clash of civilizations between the West and the Muslim world is clearly under way. Muslims have already conquered Europe and they’re not about to stop there,” he says. “Islam is on the march, we’re now in a 100-year war, and there’s no way to win because they’ll simply outbreed us.”

Mr. Allmon, who also manages more than $100 million in assets and sees a lower market by year end, says “today’s course for investors is obvious; it’s time to be very high in cash reserves.”

Or, as our two worry-warts see the current scene: Beware the Ides of September.