Moving with the same entrepreneurial alacrity that built William Paley's CBS, David Sarnoff's RCA and Jules Stein's MCA, Rupert Murdoch is taking his boldest step yet to transform his News Corp. Ltd. into a vertically integrated global multimedia giant.

Metromedia Inc. announced yesterday that it had agreed in principle to sell its seven TV stations to a company formed by Murdoch and businessman Marvin Davis, who in turn will sell one of the seven to Hearst Corp. The six remaining stations -- all in major U.S. markets -- would be the video crown jewels in an acquisition that could make Murdoch the first broadcaster to own television networks on three continents.

In Australia, Murdoch owns the Nine Network. In Europe, he owns Sky Channel -- a fledgling satellite superstation that beams English-language programming to more than 3 million households throughout the continent.

Should the acquisition be approved, Murdoch would own vital channels of video distribution; his recently acquired 50 percent stake in the Twentieth Century-Fox movie studio makes him a major player in film and video production as well. In less than a year, Murdoch's News Corp. would thus become a major vertically integrated film and video company with global distribution.

Vertical integration means the expansion of a business through the acquisition of other firms that are engaged in either earlier or later stages of production or distribution of the same product.

The Metromedia deal adds an ironic postscript to Hollywood's successful fight to block the major commercial television networks from increasing their role in television and movie programming. Murdoch effectively would achieve the same ends by having Hollywood buy the network. The speed and boldness of the transactions are less the results of a grand strategy, however, than the swift response to an opportunity.

"A lot of people claim they have 10-year plans or five-year plans or something," Murdoch said in a recent interview with Folio magazine. "But basically, the most successful businesses are opportunistic and you take your opportunities when they come."

As his acquisitions of The New York Post, New York magazine, The Times of London and The Chicago Sun-Times have demonstrated, Murdoch is willing and able to move boldly and pay top dollar to assure that a deal is consummated.

Detractors accuse him of a certain ethical elasticity when it comes to keeping promises of editorial independence. He also is accused of encouraging his newspapers -- notably The New York Post and The London Sun -- to practice a brand of sensational tabloid journalism. On the other hand, he has left The Village Voice and New York magazines alone.

In many respects, Murdoch is one of the last of the old-fashioned media figures able to rule their companies by whim. Unlike today's leaders of CBS and RCA, which are publicly held and thus subject to shareholder and takeover pressures, Murdoch retains control of his News Corp. and its daily operations. While he does delegate most day-to-day operations of his global holdings, he relentlessly prods his subordinates around the world with suggestions and criticisms.

Murdoch's drive to achieve a broad-based multimedia company led News America -- News Corp.'s U.S. subsidiary -- to pay $350 million for the Ziff-Davis Business Publications last year and roughly $250 million for a 50 percent share of Twentieth Century-Fox this March. The Fox venture gave Murdoch movie production capacity he has long craved.

Murdoch has made no secret of his multimedia ambitions in this country. Last year, he undertook a hostile bid to wrest control of Warner Communications Inc., a diversified communications company that owns Warner Bros. Studio. The bid failed, but Murdoch walked away with more than $40 million in a greenmail settlement.

Hoping to launch a new space-based television network, Murdoch spent millions of dollars in an aborted effort to create a direct broadcast satellite-to-home television network that would have required viewers to buy a special satellite receiving dish. The plan was abandoned early last year as both the cost of the dishes and the complexity of the logistics proved far higher than expected.

However, Murdoch's $10 million acquisition of Sky Channel in 1983 has proven more successful, as Europe's cable television penetration continues to rise and multinational companies grow more willing to advertise on continental television networks.

The Metromedia stations will cost Murdoch more than cash. He will have to abandon his Australian citizenship, because foreign ownership restrictions permit only U.S. citizens to hold a major share in American broadcast properties.

It is unclear whether Murdoch would or could bring to his new U.S. television stations the brand of "tabloid television" that is used to describe his European television operations.

But if the acquisition succeeds, Murdoch will have catapulted a company best known for newspapers into one that might become best known for its television and its movies. Indeed, Murdoch may succeed in intensifying competition in local television markets.