On the eve of its second century, Sears, Roebuck and Co. is looking more than ever to its future.

"We're not looking back," said Sears' President Edward A. Brennan, the man who is slated to become Sears' chairman on Jan. 1, 1986, the same time the company officially marks its 100th birthday. "We are the premiere retailer in the world. We intend to stay that way."

Brennan, 51, who joined Sears in 1956 selling ties, underwear and pajamas in the men's furnishings department, has been credited by the retailing community for the massive upgrading of the company's stores and merchandise in recent years. After a career that saw him rise rapidly through the ranks, moving nearly every three years to new jobs throughout the operation, Brennan was picked to head Sears' retail operations in 1980.

Brennan was named president of all Sears' operations 15 months ago, virtually guaranteeing at the time that he would become head of the nation's largest retailer when Chairman Edward R. Telling retired.

When Brennan takes over as chairman two months from now, he will preside over a retailing giant that is more than just a chain of 800 stores. In addition to its retailing operations, which account for more than two-thirds of its $39 billion annual revenue, the Sears empire includes Allstate Insurance Co., the Dean Witter Reynolds investment house, the Coldwell Banker & Co. real estate firm, and the new international trading company Sears World Trade Inc.

In a recent interview, amid the hoopla of the company's centennial celebration, Brennan talked about the future of the corporation and its evolution as a major financial force in the lives of the American consumer.

That evolution began under Telling, who has served as chairman since 1978. During his reign, Telling has tried to make Sears the ultimate one-stop shopping center. Through its acquisitions of Coldwell Banker and Dean Witter, Sears has built an empire in which a customer can buy a house, finance it, insure it and then furnish it all through one corporate entity.

Brennan, having worked closely with Telling during Sears' transformation, made it clear that he doesn't plan to make any major changes during his tenure as chairman. "I've worked with Mr. Telling on a very close basis over 15 years," he said. "I wouldn't expect there would be a great deal of change. . . . You will have change as time goes by, but there will be no dramatic change in direction."

As a cornerstone of its financial services goals, Sears is now trying to be a major credit-card provider.

"Our feeling is that, over the long term, the plastic card will be the vehicle by which people conduct their financial transactions," Brennan said to explain why Sears is spending millions of dollars to launch its own credit card, Discover.

The card is being tested in Georgia and Southern California, and is scheduled to be offered nationwide next spring if the testing goes well.

Discover is more than just a traditional credit card, accepted by restaurants, airlines, some stores and a variety of other businesses for services rendered, Brennan emphatically pointed out. "More important, it is a savings and investing vehicle," he said. Among other things, the card can be used to set up a family savings account in which interest rates would rise as the balance increases. The card also could enable a person to set up a self-directed Individual Retirement Account with Dean Witter with no set-up fee.

Armed with a host of bargains to lure customers -- including gift certificates at Sears, discounts at nationwide hotels, airlines and restaurants, and lower monthly interest charges on revolving credit balances -- Sears eagerly is courting customers as well as merchants to accept Discover.

Brennan keeps very close tabs on the experiment, receiving daily figures on the number of new customers and merchants. As of late October -- about two months after Sears started the test in Georgia -- more than 145,000 consumers had signed up to use the card, while 3,340 merchants had agreed to accept it. For the most part, however, major department stores have refused to join the bandwagon, fearing that they would be helping a major competitor by accepting the Discover Card. Only Dayton Hudson Corp., which owns a variety of department and discount stores, and Montgomery Ward -- where the chairman is Brennan's brother -- have announced they would accept the card.

Nonetheless, Brennan remains confident that Discover will be successful. "We always knew it would be a great challenge," he said. But considering that Sears has signed up about 50 percent more customers than it had anticipated by this time, "It is not as great a challenge as we thought it would be," he said.

Still, he admitted, "It's going to take a while for actual use of these cards -- for it to be the No. 1 choice." It also will take a while for the card to add any profits on the bottom line. Brennan previously had said that Discover would not be profitable until 1988 at the earliest. "It is too early to reassess that," he said.

Just as Sears is trying to be a major credit card company, it also plans to be a dominant home mortgage firm. "We intend to be a very major provider of home mortgages to the American public," he said.

To achieve that goal, Brennan plans to greatly enlarge the role of its real estate subsidiary, Coldwell Banker. When Sears acquired Coldwell Banker in 1981, it accounted for 4 percent of the nation's home sales, Brennan said. This year, it accounts for 8 percent. "I think we can build that to 20 percent by the early 1990s," he said. If so, Coldwell Banker would be selling more than 500,000 houses a year.

"In every one of these home sales, mortgages need to be secured," Brennan said. "We intend to provide an opportunity to home buyers of a very competitive mortgage" through Coldwell Banker. Dean Witter then would package these mortgages into securities and sell them to financial institutions, Brennan said.

Despite the increased emphasis on financial services, Brennan has not forgotten his retailing roots: He listed a host of products Sears had developed for its centennial year. "We have everything from new tires to a new wool carpeting in an array of colors to a new top-of-the-line dishwasher that will wash dishes cleaner than any in the market," Brennan said.

"One of the most fascinating is a new paint that is in a semi-solid state, sold in a 'box.' When applied by a roller or paintbrush, it liquifies, so there is no dripping. It is truly a dripless paint," said Brennan, continuing to be the consummate salesman, which has accounted for much of his success at Sears.

Another product that Brennan pointed to proudly is a voice-activated speed controller for cars that allows a driver to set a cruising speed and raise it or lower it merely by speaking.

These and about 12 dozen other products will be introduced as part of the Sears' centennial celebration over the next year.

The festivities come at a time when competition in retailing has never been fiercer. On the one hand, Sears and other general-merchandise retailers are faced with a rash of discount and off-price stores that offer a wide assortment of merchandise at relatively low prices. On the other hand, the traditional retailers also must duel with the increasing number of specialty stores that offer an in-depth assortment of a limited line of goods. As the department stores and general-merchandise chains fight these two types of retailers, they also must battle one another to hold on to their own market share.

The increased competition, coupled with a sluggish economy, clearly is making an impact on the company's bottom line. For the first nine months of this year, Sear's profits have fallen by 15.7 percent to $751 million from $891.7 million for the first nine months of 1984.

With a recent slight pickup in retail sales, Brennan says he is confident the worst is over. "We believe we will see some improvement in the consumer sector as we move through November and December," he said. And despite some predictions by retailing economists that the economy should hit a low point and pause late next year, Brennan is optimistic about 1986. "What we see through 1986 is a fairly healthy environment; it should be a good year for retailers," he said.

Brennan is even more bullish about the company's long-term future. "The next 100 years will be great," he said. "Sears will be a great company."