How secure is US lead in the sunbeam race?

Will the United States not be nimble enough to win the race for economical solar power?

Direct conversion of electricity from the sun (photovoltaics) is still too young a technology to reap big profits. Nevertheless, it has shown enough promise to catch the fancy of some high-stakes players: Exxon, Atlantic Richfield, and foreign governments, to name a few.

The US is currently world leader in photovoltaics, cornering 85 percent of world sales. France, West Germany, and Japan share the remaining market slice.

But some critics feel the American photovoltaics industry - dominated by a few companies infused with oil money - is becoming sluggish. Combined with the virtual elimination of federal solar support, the US risks falling behind foreign competitors, they say.

''We must ensure that we do not trade energy dependence on the OPEC nations for dependence on the Japanese, French, and German photovoltaic firms,'' says Barrett Stambler, author of a just-released report on competition in the photovoltaics (p/v) industry. Concern over concentration in the US p/v industry is not new. In 1980, the House Small Business subcommittee on energy found that 77 percent of the domestic market was controlled by three companies.

A new study, carried out by the Center for Renewable Resources by request of the US Small Business Administration, has found no slackening of the trend toward top-heaviness.

Four companies - Solarex Inc., Arco Solar, Solar Power Corporation, and Solec - control 86 percent of photovoltaic sales, the report says. Ten others scrap for the rest.

Three of the four big boys are partly or wholly owned by oil companies. Solar Power Corporation is a subsidiary of Exxon; ARCO Solar a part of Atlantic Richfield. Solarex, the No. 1 producer, is partly owned by Standard Oil of Indiana; but Dr. Joseph Lindmayer, the company's president, says the interest is ''less than 30 percent'' and denies he is controlled by oil interests in any way.

The industry has grown steadily, from $12 million in revenues during 1978 to report.

And small solar research firms may be stiff-armed by industry leaders through predatory pricing, it says. It cites allegations that ARCO Solar has offered p/vs at unfair prices in an effort to buy market share, in one instance, bidding

''We do not predatory-price,'' an ARCO Solar spokesman replies. In any case, he says, they have sold nary a thing in France, where the strongest foreign competition lies.

The current makeup of the US p/v industry, as detailed by the Center for Renewable Resources report, portends two related trends:

1. It will become harder for new producers to jump into photovoltaics. As a result, the US industry will lose a key source of innovative spark and competition.

Not everyone thinks this will be a problem. The current concentration of companies at the top ''shouldn't be very much a matter of concern,'' says Crawford Honeycutt of the Department of Energy office of competition. ''There isn't room for many producers right now. It's a normal way for an industry to start out.''

Experts have estimated it takes a new company anywhere from $2 million to $30 million to stake a claim in photovoltaics. But as technology becomes more complex, these capital costs could skyrocket.

For prospective entrants, ''it's going to be difficult to get in because a lot of investment goes into this field,'' says Dr. Lindmayer at Solarex. He estimates it now costs $50 million to mount a strong charge into p/vs. Claiming that semiconductor manufacturers and other electronics firms are just biding their time before going solar is ''wishful thinking,'' he says.

2. Oil-dominated solar subsidiaries may not press hard to develop a technology that competes with petroleum.

This conflict-of-interest issue involves a lot of emotion.

''I don't think it's a problem oil companies are involved in the industry now ,'' says the DOE's Mr. Honeycutt. ''A lot of us recoil - but if oil companies were not in there, who would be? We may have a gut feeling against it, but without the oil companies the p/v market would be even smaller than it is today.''

On the other hand, Rep. Berkley Bedell (D) of Iowa says it's a valid concern.

''If we think for a minute the oil companies will go ahead and develop something to compete with their oil . . . how dumb do we think they are?'' Representative Bedell says.

In the end, critics fear, a sluggish US industry will be outsprinted by foreign competitors. A proposed slash of 64 percent in federal aid for photovoltaic research and development won't help, they say. And, since the first big market for p/vs will be in developing countries, cuts in export promotion funds may hurt even more.

''It's clear there's going to be an explosion of the financial viability of p/v systems in the third world,'' Mr. Bedell says. Foreign competitors will donate model village systems, lend money at low rates, and generally support p/v exports, he says, while the US stands idly by.

''We're going to see Japan, France, and Germany walk away with those markets'' unless the US changes its attitude, Bedell claims.

Foreign producers could use third-world experience to develop their domestic markets.

''And when it becomes economic to sell it in Japan, guess where else it will be selling?'' a congressional aide says.