It sounds like common sense: If you're selling VCRs and compact disc players, why not also sell the videos and CDs that play on them?

Japan's Matsushita Electric Industrial Co., the world's largest consumer-electronics company and the maker of Panasonic and Quasar brand equipment, is paying $7.5 billion in pursuit of that simple proposition. In announcing its buyout of MCA Inc., the Los Angeles-based entertainment company, Matsushita said Monday that it was seeking to combine MCA's entertainment "software" -- movies by Steven Spielberg, recordings by Elton John -- with its endless array of "hardware."

"Software and hardware have been developing simultaneously," said Matsushita President Akio Tanii. "They are like wheels of the same car." With Matsushita churning out the boxes and MCA's Universal Pictures and Music Entertainment Group churning out the hits, the combined companies, said Tanii, will be able to create "synergy" -- the whole exceeding the sum of the parts.

But buzzwords like "synergy" and "vertical integration" may be nothing more than that. Integrating the assembly line with the studio may someday revolutionize the marketing of new technologies such as high-definition television sets and laser disc players, some observers say, but for now the idea remains largely unproven. In fact, two other giant electronics firms, Sony Corp. of Japan and Philips NV of the Netherlands, have run software divisions alongside their manufacturing operations without realizing any special benefits.

"I have always been at a loss to see what difference it makes," said Karen Firestone, who manages Fidelity Investment Group's entertainment division. "CBS Records is still trying to find the best acts and Sony is still trying to make the best audio equipment. But I'm not sure what incentive one has just because the other one is around."

Firestone suggests foreign acquisitions of Hollywood companies, such as Sony's $4.8 billion acquisition of Columbia Pictures last year, make sense whether or not there's synergy. The major U.S. studios, she said, produce a unique and profitable product that other countries have not been able to replicate. But, she added, "creative" businesses are mercurial: "What if no one wants to watch the movie Columbia makes?"

Sony's $2 billion acquisition of CBS Records in 1987 has by all accounts been a profitable one, but for reasons other than selling Walkman cassette players. The label, whose artists include Bruce Springsteen and Michael Jackson, has benefited from the worldwide surge in music sales fanned by the compact disc player -- a boom that began in 1982, five years before Sony bought CBS Records.

At the same time, Sony has been reluctant to use its clout in the software and hardware markets to spur faster adoption of digital-audio tape players. The Japanese parent company took a hands-off approach when CBS Records executives joined the record industry in refusing to issue prerecorded digital tapes until manufacturers implanted a special microchip to prevent DAT machines from being able to make multiple recordings. CBS Records has since issued a limited number of DAT recordings.

The integration of CBS Records and Sony's manufacturing operation "hasn't happened to the degree that would have expected," noted Leonard Feldman, the senior editor of Audio magazine.

Similarly, Philips's ownership of Polygram Records does not appear to have made much difference to its consumer electronics group, which sells products under the Magnavox and Sylvania brands. Although Philips's consumer electronics sales have recently rebounded, the division was operating in the red earlier this year. Philips has a minimal share of the compact disc market today, despite having invented the CD.

Larry Gerbrandt, senior vice president of Paul Kagan Associates, an entertainment research firm in New York, said so-called vertical integration is necessary for companies such as Matsushita if they want to keep pace with Sony in determining technical standards for entertainment software. Sony, for example, might have been able to establish its Beta videocassette format as the VCR standard had it been able to convince producers to release movies only in that format. But now that both Sony and Matsushita own their own film libraries, neither could make such a move by itself.

"The Japanese realize HDTV is coming five to 10 years from now, laser discs are coming five to 10 years from now," said Gerbrandt. "There's already a growing format battle" in the camcorder market. "... they want to at least neutralize {the other's} advantage," he said.

So far, companies that have built entertainment and media conglomerates around movie, record and TV production and book publishing, have seen only limited interplay among their various software divisions. In theory, such companies were to have been one-stop shops: A book property, for example, could be made into a movie and then a TV series, which then could be sold in syndication or on videocassette.

However, the idea has succeeded only rarely -- with the much cited exception of Paramount's "Star Trek" characters, which have appeared in five movies, dozens of books and in two TV series, all produced within Paramount; the company even owns some of the local TV stations that play "Star Trek" reruns and its first-run sequel "Star Trek: The Next Generation."

Laurence Tisch, CBS Inc.'s chief executive, was so dissatisfied with CBS's entertainment-conglomerate strategy that he sold off its magazine and record divisions to concentrate strictly on TV and radio broadcasting.

Staff correspondent Paul Blustein contributed to this report from Tokyo.