NORTHERN IRELAND

The doors of the public buildings in Belfast are paneled in one-way glass. You don't see the security guards inside as you aproach: You only see yourself in the mirrored sheen.

The glass, like the barbed wire and the street-corner soldiers, is simply one more response to the well-known sectarian-based but politicaly motivated campaign of terrorism now in its tenth year and euphemistically known as "the troubles."

Yet the glass is also a symbol. For Belfast, capital of the six northeastern counties of the Emerald Isle which constitute Northern Ireland, or (not so accurately) Ulster, is an excellent mirror: It reflects back whatever image the visitor brings to it.

To those who come primed with news media accounts of bombings and snipings, this city of 400,000 is a grisly derelict. Blasted buildings, chain-link fences , helicopters, and police checkpoints are never far from view. The last remaining major downtown hotel, the Europa, offers its friendly and comfortable accommodations within a fenced compound where guards with explosive-sniffers frisk incoming guests.

Within view are other accommodations. The Divis Flats, not 15 years old and already a high-rise planner's nightmare, dotted with plywood-covered windows and graffiti, are set in a wasteland of discarded boots and broken bricks. They stand near what is called (also euphemistically) the "peace line," where Roman Catholic West Belfast butts up against the equally grim landscape of its Protestant neighbor, amid the nettles of sectarian violence. Low buildings here have barbed wire looping along their roof edges. Tall ones have garish orange flood- lights bathing the empty streets beneath.

But visitors primed with information about industrial development see another face in the glass. Here, they are told, is a region making a mighty and not unsuccessful effort to draw investment from Western Europe and America. Here are the kinds of financial incentives businessmen find hard to refuse: an amiable and disciplined work force eager to reduce the country's 11.5 percent unemployment, a well-developed infrastructure of roads and ports, ample power and water, new factories awaiting occupancy, and a government falling over itself to provide businesses with grants, loans, rent-free premises, and training programs.

Some big American names have come already: Du Pont, Ford, Goodyear, and General Motors. Some dazzling new ventures are in the works, most notably the De Lorean car plant. And some solid smaller companies, like Hughes Tool, are clicking along smoothly and have no thought of leaving.

Many companies bring their own top management for the first few years, who find around Belfast an easily accessible area of green pastoral beauty where yacht basins and golf clubs lie along streams bringing salmon and trout up to the weekend fly fishermen. They also find, despite press blarings, a murder rate significantly lower than in many American cities, a police force skilled in public relations and having no complaints about underfunding, and areas of spaciously detached houses more american than English in appearance.

Nearby are schools whose children, according to Northern Ireland Office surveys, have a higher rate of success in the nationwide O-level and A-level examinations than do their counterparts in other areas of the United Kingdom. Here they find a community eager to thrive -- alert to its common enemy and in many ways more cohesive ans less apathetic than in some of the English regions where unemployment is nearly as high.

Which account is true? What lies behind the glass? Is this a terrorist's playfield or a manufacturer's El Dorado?

The answer, it seems, falls between the two -- and probably further toward the latter than ever in the past 10 years. Brian Lyttle, deputy secretary of the Norhtern Ireland Department of Commerce, explains that "the situation as regards new investment has changed quite dramatically since 1978."

The international competition to attract new foreign manufacturing to English- speaking areas of the European Community is a polite game, played in potent earnest against professionals in the Republic of Ireland, Scotland, Wales , and the English regions. The rewards to investors -- low unit costs and a tariff-free entree into a European market of 259 million consumers -- balance the rewards to the host countries, where much-needed jobs are created. Between 1970 and 1977, however, because of the troubles, "we virtually disappeared from the investment market," Mr. Lyttle says.

But the intensity of the troubles scaled down in 1977, with civilian killings only 28 percent of the previous year's level. That year the police and the Army changed tactics. That year, too, the government bolstered its incentive program for new businesses.

"Armed with this package, we had to get ourselves back inside the door with American corporations," Mr. Lyttle says.

Since the last survey by this newspaper (May 1978), the results have been improving. The department claims that its programs helped create 4,000 promised jobs in 1978, 2,700 in 1979. Announcements of a General Motors expansion and a new Lear Jet factory have added 1,850 so far this year.

But, Mr. Lyttle adds, these figures must be seen in perspective. Aside from the troubles, the problems in Northern Ireland are typical of those of the United Kingdom in general: a strong pound (making exports less competitive), high interest rates, and a depressed worldwide market in many areas. And the history of the region is similar, the prominent feature being the decline of the traditional businesses, which date back to the Industrial Revolution and are no longer invincible. In the past 25 years, Northern Ireland has lost some 100,000 jobs in textiles, clothing, and shipbuilding.

The pressure on employment continues, compounded by the highest birthrate per thousand (16.5) in the United Kingdom (which averages 11.8, in 1977 figures).Government officials are reluctant to say how many jobs the area needs to survive. The conventional wisdom here, however, puts the figure at 10,000 a year -- well above the numbers recorded by even the most friendly statistics.

In fact, however, the situation cannot be seen apart from the troubles. The Commerce Department's first job is to convince potential investors that doing business here is, as Mr. lyttle says, "not horrendous." In this he has the support of corporations already here. This correspondent, speaking with a number of executives in small and large businesses, found that:

* Most industries, aside from the unusually tight plant security, appear to run quite untouched by the difficulties."We find that the so-called troubles have not had any great impact on industry here," says Eric Jones, engineering manager at Hughes Tool Company.

* Labor relations, measured by days lost per year, are significantly better than in the United Kingdom, the United States, or the Republic of Ireland -- although far from the impressive record of West Germany.The terrorist have no popular following here, and sympathy strikes are no longer occurring.

Managers, who often have only one or two unions to deal with, generally agree with Walter Carruthers, managing director of the Ford plant here, that, "on the whole, I think it's probably better" than it would have been had Ford in 1964 chosen a site elsewhere in Britain -- although, he adds, "It's not as good as some would have you believe."

* Most work forces are integrated. Of the 1.5 million Ulster population, Protestants make up about two-thirds and Roman Catholics one-third. By law, employers cannot discriminate. But work forces tend to reflect the sectarian mix of the areas in which plants are situated, since the typical immobility of the British worker is heightened here by fears among Catholics of traveling to work across Protestant areas, and vice versa.

While the two sects may antagonize each other by night, however, by day they are less loyal to heredity than to their trade unions.

"If you scratch the surface of any of us here," admits an Irish executive in an American company, "you'll find we're either green or orange." But work, Mr. Carruthers observes, is another story. "It's almost like therapy to them," he says, noting that both the shop floor and the company's social club are essentially trouble-free.

* Personnal security is still something that corporate executives talk about only privately. They speak of solid doors, bulletproof glass, different routes to work each day, and personal firearms. But they hasten to add that such measures are minimal.

"If I felt any serious concern for the safety of my family, I wouldn't be here," says the American director of a large company.

The executives emphasize that the problem is certainly not religious, and not even broadly political, and would agree with a government official who said of the terrorists that "they're not purging some corrupt society in the name of purity and brotherhood -- these are petty thugs." And, while three of the many killed in the past decade have been prominent industrialists, the record of business success here has been keyed to the more normal factors: how sharp the management is, how good the product.

One thing is sure: There is plenty of room for expansion. And, because inward investment (from outside of Northern Ireland) has accounted for 35 percent of Northern Ireland's jobs since 1945 (compared with 16 percent in Scotland), there is plenty of welcome for such undertakings.

The two-year-old push for new business seems to be working. According to David Hume, resident vice-president of Citibank, the prospects are better than they were in 1978. "Several companies have come in and tested the temperature of the water and found they liked it," he says. He expects more in the future.

One government official summed up the importance of inward investment. With his pencil, he circled again the northeast corner of Ireland on a small map as he spoke almost broodingly. "If we could demosntrate to ourselves that this entity was thriving and bustling," he said, "then that in itself would promote a feeling of trust and good will." Northern Ireland would no longer be on a "slippery slope," and would experience "not the vicious circle but the virtuous circle."

As he spoke, a helicopter from the Army base next door thumped away into the distance.