SAN FRANCISCO – Once again, stockholders are getting a harsh reminder that the worst time to make an investment decision is when markets are in crisis.

The dramatic collapse of Lehman Brothers and the hurried sale of Merrill Lynch over the weekend saddled investors with even steeper losses on Monday, but securities regulators moved quickly to reassure individuals that their brokerage accounts are safe, and investing veterans said that perspective, not panic, is in order.

“It’s too late to panic,” said Zachary Karabell, president of independent consulting firm River Twice Research. “And if it’s too late to panic, it’s probably time to calmly look at what’s going on in light of opportunities.”

“Selling doesn’t recoup your losses,” he added. “It just realizes them.”

When an institution of Lehman’s size and clout goes under, it’s understandable to wonder if your money is safe.

In a word, yes.

“I don’t think anybody’s money in accounts is at risk,” Karabell said. “There’s no reason to be running down to your bank or phoning your broker.”

Customers of credit unions also are protected in a worst-case scenario, said Daniel Penrod, an analyst for the California and Nevada Credit Union League, an industry trade association.

As with the FDIC insurance that guarantees bank deposits, credit union savings are insured up to $100,000 per account and $250,000 for individual retirement accounts.

“While credit unions were not part of the disease, we’re definitely dealing with the symptoms,” Penrod said. “But for the most part credit unions are showing great strength in their capital reserves.”

Regulators also looked to keep investors calm. The Securities and Exchange Commission said it’s taking steps to ensure that Lehman clients will not be adversely affected by the firm’s collapse.

The SEC said the Securities Investor Protection Corporation, a four-decades-old insurance plan for brokerage accounts, would cover the broker-dealer’s customers in a worst-case scenario. SIPC rules provide coverage up to a maximum of $500,000 per client, including a maximum of $100,000 for cash.

SIPC has not had to safeguard Lehman accounts, said Stephen Harbeck, SIPC president and chief executive.

“This demonstrates that the system works,” he said. “Customer assets have been properly segregated at Lehman Brothers; that’s why there’s been no need for SIPC to take action, but if the facts change, we’re ready.”

In announcing bankruptcy, Lehman made it clear that only the holding company was making the filing. Shareholders in Neuberger Berman, the firm’s mutual-fund unit, and Lehman Brothers Asset Management will not be impacted, Lehman said.

Separately, Merrill Lynch has agreed to be acquired by Bank of America for $50 billion.

Merrill Lynch’s customer accounts shouldn’t be affected by that transaction, as the deal is a straightforward acquisition.

U.S. stocks are down almost 25 percent since their October 2007 peak and clearly in the grip of a bear market. But this is hardly the first, or the worst, bear market that investors have suffered.

In the last seven bear markets, the Standard & Poor’s 500 Index tumbled an average of 33 percent, according to S&P.

“We are probably more than halfway through this overall bear market,” Sam Stovall, S&P’s chief investment strategist, wrote in a research note to clients. Yet his prediction lacked firm conviction, and he left open the possibility of a “mega-meltdown” decline of more than 40 percent.

“As a result, I wouldn’t try to be a hero and start a major buying campaign,” Stovall said.

“Ignore the market for a few days,” added Matthew McCall, president of Penn Financial Group LLC, a registered investment adviser. He agreed that investors “shouldn’t be doing any buying.”

Financial stocks especially should remain off limits for now, McCall said. Instead, he suggested looking at brand-name, non-financial stocks that might succumb to selling pressure. As an example, he pointed to medical-equipment makers and biotech firms, including Johnson & Johnson.

Indeed, shares of big consumer-sector giants such as Johnson & Johnson and McDonald’s lost much less than the market on Monday, and Coca-Cola’s stock was higher.

“The fundamentals will come back into play when this panic is gone, and that’s when you want to do some buying,” McCall said.

Karabell, the market researcher, agreed that investors should be in no rush to buy, but that nosing around the financial sector makes sense.

“I don’t think the financials are things you ought to be in unless you’re comfortable not looking at it for two years,” he said. “If you bought a financial-sector exchange-traded fund today, you’re going to look back in two years and say ‘How great that I bought in the summer of 2008,’ but that doesn’t mean it doesn’t go down another 25 percent from here.”

Indeed, the never-ending tug-of-war between risk and reward always disrupts investors when anxiety and uncertainty get the upper hand. But now is not the time to overhaul your investment portfolio, said Scott Kays, an Atlanta investment adviser.

“So much of the damage has already been done, any moves you make at this point could be counterproductive,” he said.

If you must sell, do so gradually, Kays suggested. That way, if the market goes down you won’t be hurt as much, but if it goes up you won’t miss out on the upside.

And if you invest with the help of a broker or a financial adviser, stay in close contact, Kays said.

“We’ve seen several downturns of 35 percent to 50 percent,” he said. “This downturn is relatively mild so far compared to previous ones. But it could happen. Can you deal with it? If you can’t, now’s the time to talk – not after the market is down 35 percent.”