Japan's largest computer maker made its most significant foray to date into Europe yesterday when Fujitsu Ltd. purchased an 80 percent stake in Britain's flagship computer firm, a move that solidifies Fujitsu's position as the world's No. 2 computer maker.

The announcement by Fujitsu that it intends to buy a controlling interest in International Computers Ltd. (ICL) for $1.27 billion is widely viewed as a step that will give the Japanese electronics giant an important foothold in manufacturing and distribution as Europe moves toward economic unity -- and perhaps increased protectionism -- in 1992.

"Just in case there is a 'fortress Europe' ... Fujitsu is covering its bets. They need a European marketing platform," said Ulric Weil, a Washington computer industry consultant.

The move also spotlights the challenges facing European computer companies as they struggle to compete in an increasingly global marketplace. While several European companies have been able to capture strong positions in their own countries, they have been losing ground when forced to compete across the continent, let alone the world.

"Very few European vendors have the presence to succeed long-term in the emerging environment. They don't want to cede it, but they may have little choice in the matter," said Donald Bellomy, an analyst of worldwide market trends for International Data Corp. (IDC) of Framingham, Mass.

Just yesterday, Groupe Bull, the major French computer maker, announced a loss of $331 million for the first half and said it expects to eliminate 3,000 jobs this year. Recently, N.V. Philips of the Netherlands said it expected an annual loss of roughly $1 billion and planned to cut 10,000 jobs. Earlier this year, Siemens AG announced plans to swallow up a smaller German computer company, Nixdorf AG.

U.S. firms, led by International Business Machines Corp., have been strengthening their position in the European market for mainframe computers -- machines costing $1 million or more -- rising from 71 percent in 1988 to 81 percent in 1989, according to IDC. The trend is similar in the market for mid-size computers, Bellomy said.

IBM is by far the world's largest computer company.

While Japanese firms hold virtually no official market share in Europe, their sales have been hidden behind European logos. Hitachi Ltd. sells computers through Olivetti, for example, and Fujitsu sells through Siemens.

Yesterday's pact between Fujitsu and ICL culminates a nine-year history of collaboration in which Fujitsu supplied ICL with key computer components. ICL, which had operating profits of $253 million last year on nearly $3 billion in sales, said its British parent, STC Ltd., now intends to shift from computers to communications technologies.

While most of its operations are in Europe, ICL has 135 employees in the Washington area who concentrate on software development. Brian Noble, eastern regional vice president, said ICL services are used mostly by large local law firms.

ICL also offers computer equipment to federal agencies, but that activity accounts for only 10 percent of its local business.

"This group been through a merger and acquisition from the other side," Noble said, referring to ICL's 1989 acquisition of Computer Consoles Inc., a software development firm. "So we understand what happens in acquisitions.

"The companies are a lot more complementary than they are competitive. We seldom run into them in our markets. So we don't expect any layoffs. We're fairly confident we will all maintain our jobs."