The office corridors are darkened; the broker's in shirt sleeves; he looks like he's been crunching numbers half the night. "Now, especially now," says a baritone voice over the images, "you need an investment firm that is rock solid."

The commercial, filmed at warp speed for Prudential-Bache Securities, will air tonight in New York and tomorrow in Washington. "We hope the tone is calm and comforting," says Peter Costiglio, senior vice president of Prudential-Bache. "In tumultuous times, we thought that would be a message of security."

Even before the New York Stock Exchange closed on Freefall Monday, brokerages and their ad agencies were huddling to plan their responses. The first print ads hit major newspapers last Wednesday; new radio and television commercials followed within two days, an extraordinarily speeded-up timetable.

The ads' common goal was not, for once, to lure new business as much as to keep current clients from jumping ship; their tone was doggedly soothing. "We wanted to kind of wrap our arms around our people," says Joan Rothberg, executive vice president of Backer Spielvogel Bates, which produced the new batch of "Rock Solid" ads. "This is nothing frivolous."

First off the dime was Merrill Lynch, which has started saying it's "still bullish on America." Originally, fans tuned into the World Series on ABC last Tuesday night were supposed to see Merrill Lynch commercials about retirement planning and college savings, complete with glimpses of the trademark bull and a soprano voice singing about knowing no boundaries. Instead, the ads were pulled and two days later, viewers saw a hastily produced 30-second videotape of the investment firm's chairman looking gravely into the camera lens and saying, "I'm here for some straight talk about the stock market."

Though the full extent of the damage was still unknown, management decided last Monday that "we have to get a message to our people," according to Charles Mangano, director of corporate advertising. "A lot of people had a lot of questions."

That afternoon, the firm "talked" to its FCs (financial consultants) across the country via satellite-transmitted videotapes. Among those who watched were the firm's ad team from Bozell, Jacobs, Kenyon & Eckhardt. Associate Creative Director Woody Woodruff worked through much of Monday night to write a full-page ad headlined "After October 19: A perspective," which ran in five newspapers the next day and featured two columns of sober analysis. Two more columns followed on Friday, when the full-page ad said, "Now, what about next week?" and announced weekend and evening hours at all branches.

Merrill Lynch's TV commercials had a similar no-frills look. The screen legend and voice-over both said, "A Message From Merrill Lynch"; the 30-second spots, taped Wednesday in the brokerage's in-house video facility, featured Chairman and CEO William Schreyer, chief economist Robert Farrell and Jack Lavery, senior vice president and director of global securities research.

All three tried to sound soberly upbeat. "Emotions can run high during market turbulence, just when reason should prevail," said the chairman (a perspective proven accurate yesterday when an armed investor shot up a Merrill Lynch office in Miami, killing a broker and critically wounding another before killing himself). Management liked the ads enough to substitute them for all its normal spots and bought extra time during Sunday's seventh World Series game.

Prudential-Bache was also groping for an advertising response last Monday. For more than a year it had used the tag line "Rock Solid. Market Wise," playing on Prudential's Rock of Gibraltar trademark. After a 508-point plunge, the decision-makers agreed, investors would be more receptive to claims of solidity than wisdom.

Newspaper ads, which featured "Rock Solid" in two-inch type, ran in 15 cities last Thursday; radio spots hit the airwaves Friday. Pru-Bache CEO George Ball will not appear in any of them, but he reportedly contributed the "Now, especially now" line. The brokerage will substantially increase its media buying for the new ads, though it won't say by how much.

To put Prudential-Bache's television commercials on the air eight days after the meltdown, "people worked day and night last week, 20-hour days," Joan Rothberg said. "People who didn't live in town stayed in town and got it done ... We did everything double-time."

The ad was written Tuesday, polished and approved on Wednesday. Locations were scouted on Thursday; the film was shot Friday at Pru-Bache headquarters at One Seaport Plaza because there was no time to build a set. The crew simply borrowed props from adjacent offices, a desk here, a computer terminal there, a briefcase from senior veep Costiglio. Just like the actors in the ad, real Prudential staffers were at work when the film crew arrived at 6 a.m. Friday and were still there when the equipment was cleared at 8 p.m. "They're probably still there," says Rothberg.

Not every investment firm pulled out the stops: E.F. Hutton, which has done its advertising in house for several years, contented itself with full-page "open letter" ads in newspapers to announce extended office hours.

Shearson Lehman Bros., however, taped its black-and-white "Talk to Us" commercial on Wednesday and put it on the air Friday. They are feeling a trifle smug at Shearson. Five years ago its ad agency, McCann-Erickson, developed a quick, cheap "tactical campaign" to respond to market changes: white type on a black background with a voice-over. "We can literally be on the air in three to four days if we need to be," says Cathleen Stewart, senior vice president for marketing. Before Oct. 19, the black-and-whites discussed rising interest rates. The current one talks about the "unsettling" and "unprecedented" events in the stock market and urges, "Now, more than ever, talk to us." The ad was produced for a paltry $7,000.

"You don't have two chances to do this," Stewart reflects. "We did get some advertising out; we could be visible. By implication, we could say, 'We're here.' "

Meanwhile, banks are jumping into the fray to promote their suddenly more attractive certificates of deposit. Chemical Bank's newspaper ad, for example, features a large head shot of a bear. "Chemical Bank," it says underneath. "For people who are finding the market unbearable."

Several agencies are already pondering the next generation of crisis advertising. It's a day-by-day decision, the ad makers watching the ticker along with everybody else, sometimes with the same sinking sensation.

"I should have gone with my feelings the week before; I was going to buy S&P 500 puts," lamented Kathy Crafts, a Bozell, Jacobs copywriter on the Merrill Lynch account. "My personal financial life was also crashing ... I was grateful we were so busy at work; otherwise I would've been crying."