By staying closed for most of last week, U.S. stock markets may have been saved from the worst of the panic-driven selling that could have followed the terrorist attacks that toppled New York’s World Trade Center.

“I think the markets will, in fact, shrug this off amazingly well,” said Donald Straszheim, vice chairman of the Milken Institute and former chief economist at Merrill Lynch & Co. While European markets initially fell sharply after hijackers flew two passenger jets into the twin towers last Tuesday, they later began to rebound.

The financial community was paralyzed by the buildings’ collapse, which brought down scores of trading firms, thousands of investment professionals and tons of communications equipment. Markets didn’t reopen all week, and it may have been a blessing.

“I don’t think it does all that much damage to have markets closed for a few days,” Straszheim said.

As the New York Stock Exchange, Nasdaq and American Stock Exchange prepared to reopen Monday morning, a number of market professionals agreed that they expect no panic-driven sell-off. But there is still some concern that the general trend of the markets which have slumped all year could resume over the coming months.

“A lot of people were initially running scared and would have sold off should the markets have remained open,” said Michael Gardner, senior vice president and directing manager of capital markets at Wedbush Morgan Securities in downtown L.A.

“You may see some initial volatility but I think cooler heads will prevail,” Gardner said.

Los Angeles companies will be among those testing the waters on Monday. Companies listed in the LABJ 200 have a combined market value of $287.6 billion, according to Duff & Phelps LLC. A loss of just 1 percent would shave nearly $3 billion off their cumulative value.

One concern is liquidity. With so many trading floors simply wiped out, traders may have a difficult time setting opening prices for small and medium-sized stocks. “L.A. has an awful lot of them,” said Peter Griffith, president and chief executive of Ernst & Young Corporate Finance LLC, based in L.A.

The NYSE, home to companies whose combined market value totals $16 trillion, may trade at a discount due to stability concerns. Long considered the most robust stock exchange in the world, the NYSE is “not the same thing as cash anymore,” Griffith said.

Some sectors of the market will surely be hit hard. Among them are airlines and travel-related industries, along with insurance companies, which are bracing for claims estimated at between $10 billion and $30 billion.

There are no airline companies based in Los Angeles, but Boeing Co. is the county’s largest private-sector employer. Boeing stock, already rattled by the slow economy, last traded at $43.46, its 52-week low. Boeing could get hit with an additional slowdown in orders for new aircraft, but the impact would be mitigated by its substantial defense and satellite operations, which could benefit over time.

In the insurance industry, some companies are expected to absorb a higher proportion of losses, said Blair Sanford, an equity analyst with Cochran Caronia Securities in San Francisco. Pasadena-based Wesco Financial Corp. is an “underutilized insurer that has the ability to prospectively provide risk capital in the wake of this disaster,” Sanford said. He thinks Wesco, 80 percent owned by Berkshire Hathaway, could be one to buy in a down market.

Walt Disney Co. is a company seen as vulnerable, along with other entertainment companies already hurting in the sagging economy.

“I expect travel to be down, which will affect the theme parks,” said Laura Martin, a Credit Suisse First Boston analyst. Disney shut its theme parks for a day, and its ABC television network has seen costs soar due to round-the-clock news coverage while forgoing advertising revenue.

Entertainment expenditures are discretionary, “and the consumer just feels like he’s been bombed,” Martin said.

Disney stock closed at $23.58 per share on Monday, Sept. 10, near its 52-week low. Other media companies with substantial entertainment facilities in Los Angeles are AOL-Time Warner Inc., Viacom Inc. and Vivendi Universal. Each was already trading at or near a 52-week low.

Investors may be looking to park money in defensive investments, such as government bonds and gold. Among stock market sectors, defensive picks include the healthcare sector.

Other sectors, such as defense, security and surveillance, are seen as opportunistic bets as the U.S. public becomes more careful about safety in the aftermath of the attacks.