Still struggling to establish its Macintosh computer as an office alternative to International Business Machines Corp. and IBM-type machines, Apple Computer Co. will introduce an enhanced version of the machine on Thursday and unveil its latest marketing tack to capture business customers.

Priced at $2,595, the new Macintosh Plus, which is faster, expandable and has more memory than its predecessor, "addresses all criticism of the Mac for business," said Apple Chief Executive Officer John Sculley. Business users had complained that the Macintosh had neither the power nor the memory to meet their needs.

"This is what Apple should have had two years ago when the Macintosh was originally introduced," said Esther Dyson, an industry consultant and editor of Release 1.0, a newsletter.

"This gives them a shot at the office market," said William Easterbrook, a San Francisco-based analyst for the Kidder-Peabody brokerage house. "It will still be pretty tough on them, but this is better than what they have."

Conceding that IBM overwhelmingly dominates the personal computer marketplace, Apple said it would continue to make it easy for Macintosh machines and IBM's to exchange information.

But Apple, which dominates the educational computer market, is counting on the emerging "desk-top publishing" market to be its gateway to the office. Desk-top publishing is the industry's phrase for turning the personal computer into a miniature, but high-quality, printing press.

Small businesses and divisions of large companies produce hundreds of reports, newsletters, manuals, presentations and other documents that could be designed and reproduced using personal computers. Apple estimates that desk-top publishing could be a $1 billion market by 1990 as companies explore the applications of computers to publishing.

"Much as xerography changed how people worked in the '60s, desk-top publishing will change how people work in the '80s and '90s," Sculley said.

Apple believes it is particularly well-positioned to corner the desk-top publishing market -- versus companies such as IBM, Xerox Corp. and Eastman Kodak Co. -- because the Mactinosh is designed to mix charts, pictures and text on a computer screen and lay out documents with relative ease. Moreover, Apple has established itself as a leader in low-cost printing technology, which enables desk-top publishers to produce professional-quality documents.

"The LaserWriter [printer] is Apple's secret weapon," said Release 1.0's Dyson. "In some ways, it's just as important to Apple as the Macintosh."

In essence, this combination of Macintosh and LaserWriter gives Apple and its retailers a complete system to sell to business users. Importantly, this desk-top-publishing approach does not yet directly compete with IBM in the business marketplace and can be a complement to existing company personal computers, Apple executives point out.

Apple's latest foray into the business market will mark the third time in five years the company has sought to loosen the grip of IBM's personal computer on small and large business customers. The company's two previous efforts -- the Lisa and the original Macintosh -- fizzled in a mess of technical limitations and marketing uncertainties. For example, the Macintosh was originally touted as "the computer for the rest of us," with no focused marketing effort for business.

"We've had many false starts with business in the past," Sculley conceded.

"I don't think we ever understood who we were marketing to," said William Campbell, Apple's vice president of marketing, who came to the company two years ago from Kodak. "We treated the business market as a monolith rather than identifying high-need segments . . . . We have literally wasted a large part of two years in pursuing the business market."

Now, Campbell said, Apple recognizes that it has to appeal to the nontraditional business buyers of personal computers rather than compete head to head with IBM.

"We're not going to get the green-eyeshade guy," he says. "Everybody who absolutely needs a personal computer already has one. We have to expand the market."

Campbell said that the Macintosh's relative ease of use and new power will attract the small-business person and Fortune 500 departments who need computers for more than "number-crunching," financial analysis and modeling.

"If I were at Apple, I'd stop comparing myself to IBM and explain why people should buy a personal computer ," said Lloyd Kvamme, formerly a top Apple executive and now a Silicon Valley venture capitalist.

But Campbell noted that IBM's personal computer has become the de facto industry standard.

Nevertheless, Apple projects that 1986 will see a 30 percent rise in the number of business personal computers sold. "It's critical for Mac's success that we get 30 percent of that 30 percent," Campbell said. But he conceded that "if I got 20 percent of 20 percent industry growth, I'd still be doing pretty good."

Apple's new marketing thrust is an outgrowth of a massive corporate restructuring last year that led to Apple's first quarterly loss, more than 1,200 layoffs and the resignation of Steven Jobs, the company chairman and cofounder.