Since the early 1970s, the nation's brokerage firms have been searching for new lines of business to smooth our their earnings because of the cyclical nature of commissions in the securities business.

Although your friendly broker still wants to interest you in stocks, today he may try to peddle life insurance, commodities futures contracts, houses, mortages, money market funds or tax shelters.

And if the broker works for Des Moines-based R.G. Dickerson Co., he may suggest an airline ticket or a weekend travel package to Las Vegas.

Dickinson is one of two brokerage firms in the nation that have entered the travel agency business. The other is Omaha's Chiles, Heider, which picked up Travel Transport from Omaha National Bank in 1975 after the Federal Reserve Board decided that the travel business wasn't one in which bank holding companies should engage. Travel Transport is one of the 10 or 12 biggest travel agencies in the country.

Edward I. O'Brien, president of the Securities Industry Association which held its annual meeting here this week, said that when investors left the stock market "in droves" in the early 1970s, "Diversification was thrust upon an industry faced with sagging demands for its basic products."

Diversification has been conrtoversial. Regulators and some brokerage officials worry that securities firms weaken their ability to serve the capital-raising process when they use scarce capital of their own in other pursuits. Firms argue that by diversifying they can even out their earnings and enhance their ability to serve investors and corporations.

J. Philip Boesel, Jr. of R. G. Dickenson, said the travel business seemed to make a lot of sense for a brokerage firm. Dickenson has an extensive list of clients. "The people you're doing business with travel a lot," be they individual clients or representatives of corporations. Because Dickenson officials travel, too, "We know the needs of the business traveler," Boesel said.

He said a Chiles, Heider official touted him onto the travel business at a securities convention in 1974 when Chiles was negotiating to buy Travel & Transport.

After searching for a firm to acquire and finding acceptable pickings slim, Dickinson decided to start its own agency.

In November 1976, the agency opened its doors. It is a subsidiary of the R. G. Dickinson Group Inc. which also owns a property management firm in addition to the brokerage house. After losing money for several years, the travel agency is profitable and is growing more so today, Boesel said. It is now the second or third largest travel agency in Des Moines, and officials anticipate sales of about $4 million this year.

But the agency made some embarrasing, and costly, mistakes along the way, Boesel said.

In 1978, the firm decided to sponsor a marathon run along the original terrain in Greece. "We envisioned it as an every-year thing" that would garner the regional broker national publicity, Boesel said. "It might have worked a year later."

But it was a bust. The agency chartered planes from New York, Chicago and Los Angeles and booked rooms in a Greek hotel. The run hoped to grab some of the big names in the running business and advertised in magazines aimed at the running public.

But of the anticipated 300 paying runners, only about 125 signed up. The charters were cancelled, and the competitors were sent to Greece on commercial flights. Hotel rooms were cancelled.

Travel agencies make their money through commissions paid by airlines, hotels, railroads and the like. They don't charge travelers a fee.

The nation's airlines are moving trough a difficult period of fare deregulation. In the process many are experimenting with the once standard commission they pay travel agents. An agency owned by a broker might fare better than most, Boesel said.