On the surface, the four rubber companies negotiating for a new labor contract appear monolithic and power.

All four are typical of the huge multinational firms that have come to dominate every major industry in the world.

They operate globally, and have diversified into a wide range of businesses, a development that has limited their vulnerability to localized problems, such as strikes in one country or in one sector of their activities.

Yet these same companies also have their special weaknesses, and individual interests, which tend to make them considerably less powerful than they seem.

The U.S. tire industry "is not economically healthy," according to a Commerce Department study drafted in March.

Productivity, which had been growing in the 1960s, declined between 1973 and 1977.

Costs of synthetics-carbon black, nylon and polyester, the oil-based raw materials that go into tires-have been rising rapidly.

Imports have captured 12 percent of the American tire market, compared with 3 percent in 1969.

At the same time, the outlook for future growth has been clouded by the advent of smaller, longer lasting radial tires, and by the possibility that as tire life increases automakers will abandon spare tires.

These developments are dramatically reflected in company balance sheets.

Goodyear, the nation's 22nd largest industrial enterprise in sales, ranked 368th in the ratio of profits to those sales. Firestone, which was forced by the government to recall most of its 500 series radial tires, lost $148 million in 1978, the second largest loss, after Chrysler, reported by any American company.

Partially offsetting some of these special difficulties in their tire operations are the diversified, global structures of the major films.

Almost one third of their $17 billion in sales in 1978 came from foreign operations not directly affected by U.S. pay scales and benefits.

And making tires is no longer their sole business. If Goodyear never made another tire, it still would rank in the top 300 industrial firms in the nation from aerospace and chemical businesses. Uniroyal and Goodrich now earn about half of all their income from businesses not directly related to tires, such as chemicals and industrial products, and both companies have indicated that these are areas that will get priority in future investment decisions.

Even so, the American tire business is central to the success of all the companies, and the current round of labor talks catches all of them in a period of unprecedented adjustment.

Goodyear, the world's largest tire company, is in the middle of a campaign to seize a larger share of the U.S. tire market through massive and costly investments in new, highly automated radial tire plants.

Financial analysts note that Uniroyal, which has been selected by the United Rubber Workers for intensive bargaining, is vulnerable on several counts.

For one thing, its tire business depends heavily on a single major customer: General Motors. Traditionally, it has been difficult for the tire companies to pass on higher costs resulting from labor settlements to the giant automobile companies. Instead, these costs are recovered in the larger retail tire market. However, Uniroyal's share of this retail market is much smaller than that of other major tire companies.

Another difficulty facing Uniroyal is the pension obligations it will have to cover out of annual operations. These now total some $676 million, about the same as Goodyear's, a company that is 3 times the size of Uniroyal.

Analysts say these problems of the major companies do not necessarily translate into bargaining leverage for the rubber workers union. The reason is that all four giant companies have been moving rapidly in the last few years to exploit their increasing diversity and multinational scope.

Uniroyal is "redeploying assets" into more profitable enterprises outside the tire business. This month, the company agreed in principle to sell its European tire plants to Continental of West Germany. At the same time, the company said it would use the funds from the sale to expand its chemical and plastics businesses in Europe.

Uniroyal's strategy has been to phase out unprofitable tire plants and to invest more in agricultural chemicals and plastics. A similar pattern of investments is being followed by Goodrich.

Some industry analysts doubt whether several old, marginally profitable tire plants would reopen if they were struck by the rubber workers.