GLENVIEW, ILL. -- Over the past four decades, Zenith Electronics Corp. has seen them come and go. Names like Philco, Sylvania, Admiral and Magnavox -- American companies that, like Zenith, made a go at the television-making business against increasingly strong competition from Japan and elsewhere.

Now only Zenith remains. Its last two American-owned competitors, General Electric and RCA, were sold last month by General Electric Co. to France's Thomson S.A. Like some of the other names from Zenith's competitive past, the GE and RCA brands will live on under foreign ownership. But only Zenith still can claim to be American born and bred.

Some would say Zenith is crazy. At a time when cheaper and cheaper televisions are flooding in from Japan, Korea, Taiwan and other East Asian nations, Zenith still is doing the bulk of its bread-and-butter manufacturing in Chicago and Missouri.

But Zenith officials believe they can be successful against the foreign competition by stressing quality, technology and careful cost cutting. The company's TV business hasn't been very profitable over the past few years -- truth be told, Zenith has lost a few million dollars each of the last two years, and it's just barely breaking even this year -- but Zenith has an ace in the hole, a fast-growing computer business that is starting to generate enough profit to carry the TV side of the company, and actually now exceeds the revenue from Zenith's TV business.

And Zenith believes it has come up with a technological breakthrough that could be a huge moneymaker in the television-set industry: a revolutionary new picture tube with a flat front the provides picture quality far superior to that of even the best traditional picture tubes, without much difference in price. The company has just begun selling the new screen -- called a "flat tension mask," or FMT tube -- as a computer monitor, and will offer it on a television set later this year.

Analysts say Zenith's ability to survive where other American companies have failed is partly attributable to its position of being solely a consumer electronics company. That allowed -- even forced -- Zenith to concentrate on the radio and TV fields while its competitors had other interests that both distracted them and gave them businesses to retreat into. In addition, Zenith has been a major player in the TV business almost since its inception, running almost neck-and-neck for the No. 1 position with RCA, even today.

"Unlike some other people in that business, that has been their principal business," said Russell Leavitt, an analyst at Salomon Brothers. "While it has been a difficult business, it probably was not as difficult for them as it might have been for somebody else who didn't have so large a position."

Zenith doesn't see anything very remarkable in being the only American company still in the TV industry. "I don't think it matters a lot," Chairman Jerry K. Pearlman said in an interview at the company's headquarters here.

Pearlman argues that Thomson's ownership of GE and RCA should make little near-term difference in the industry's competitive make-up, since Thomson has said it plans to let the American TV business run autonomously.

And regardless of the ownership of the companies involved, he pointed out, the TV industry long has crossed international borders. "It's a global business, from the standpoint of technology and input of the material building blocks," he said. "We have all been internationally affiliated for years. We buy parts internationally, we sell parts internationally. ... Everybody has got a foreign chassis in their sets."

Indeed, many of the sets with Japanese name tags are assembled in the United States, to save customs duties, while the change of ownership of the GE and RCA brands won't shift their major production center out of Indianapolis. Even Zenith is in on the game -- some of its smaller sets, as well as subassemblies for its larger TVs, are made in Mexico.

That foreign sourcing is critical to Zenith's ability to keep costs down, Pearlman said. "We have an excellent cost position for delivery to North America," he said. To help, the company has won significant contract concessions from union workers by threatening to move more production to Mexico.

Keeping costs down is critical in the TV-making business, which has been hit about as hard by low-cost foreign competition as any industry. Zenith long has been in the forefront of industry complaints about dumping of sets on the U.S. market by Asian competitors, first the Japanese and now the Taiwanese and Koreans, and the fierce price competition that drove out its American competitors also has battered Zenith's profits.

"They have exploited the market through dumping," Pearlman said of his company's Asian competitors. The numbers cited to back up his point are staggering: In the fastest-growing part of the business, TVs with 13- to 20-inch picture screens, the foreign share of the American market has jumped to nearly three-quarters -- from 25 percent in 1982. "Our belief is that those are ill-gotten gains," he said.

Pearlman hopes trade legislation will help remove the advantages and bring costs to foreign manufacturers more in line with those of American makers, so that prices -- and profits -- will go up. "It's a business that needs to have the anchor of Korean pricing raised," he said. "The entire industry needs a price increase."

In lieu of that, Zenith is trying to gain a competitive edge on the technology front, with flat tension mask tubes as the chief weapon. Unlike regular TV tubes, FTM screens have a perfectly flat face, which all but eliminates glare and dramatically improves contrast and picture quality.

As prices of the FTM tubes come down to a level competitive with existing screens over the next couple of years, Zenith officials think they will have a big winner. They have offered to license the technology to competitors, who so far have been wary, since similar technology has been on the drawing boards at other companies in the past, with little success. "Everybody's waiting to see if we can really produce it," Pearlman said. "But we can. We are."

While TVs have long been Zenith's strength, the company also has quietly become a formidable force in the computer business. Zenith will sell more than $1 billion worth of computers this year, twice as many as a year ago, and as much revenue as the company will bring in from its TV business.

Zenith, which moved into the computer business in the late 1970s, has made it where other large electronics companies seeking similar diversifications have failed by targeting markets others had neglected -- particularly the huge government market for personal computers.

Zenith made an early decision to let other companies fight it out in the business computer market while it sold machines to government and university customers. By doing so, it figured, it could save its advertsing budget and spend the money on technology that those specialized markets would appreciate and on keeping prices down. "We said, where can we spend money only in relation to our volume and find a customer who will appreciate our technology?" Pearlman said. "We said, we'll go after them with super hardware and price. ... We said we'll take what we would have spent on advertising and use it on the cost of the machines."

One of its biggest breakthroughs in the federal market occurred last year, when it won a contract to supply 15,000 portable computers to the Internal Revenue Service.

The company also has attempted to avoid getting into "me-too" parts of the personal computer business, where one company's machine is pretty much like another's, by offering features not found elsewhere. So, while Zenith computers are IBM compatible, they are distinguished from the competition by price, ease of use and such features as the FTM screen and Zenith's huge-selling portable lap-top computer. "Differentiating products are important to get out there," Pearlman said. "We have always tried to provide more bang for the buck ... and that's been a big help in trying to deal with the more sophisticated customer.

"Just doing an IBM copy leaves you with only one marketing strategy, and that's price," he added.

Zenith gets high marks from analysts for its computer strategy, and for its success in using the computer business to cover hard times in the TV field. "They've successfully developed a nonconsumer business in the computer and components business ... and it's growing at a phenomenally good rate," said Charles Ryan, an analyst at Merrill Lynch & Co.

"It gives them some balance that prior to that they didn't have," Leavitt said.

And the analysts are optimistic that the company's TV business is headed for earnings improvement as foreign makers deal with new trade laws and currency revaluations. "I think they're on the threshold of some earnings gains," Ryan said.