For years, consumer advocate Ralph Nader and people of like mind have began pressing the government to underwrite the development of solar power as an alternative to the traditional forms of energy, dispensed by American industry.

Finally the government has responded. Spending to aid solar development will reach almost $500 million this year - up tenfold in five years - and promises to grow by hundreds of millions next year.

But Nader isn't happy.

To his chagrin, a group of Fortune 500 giants ranging from Atlantic Richfield to Westinghouse has taken up the solar cause. The large corporations of which he is so wary have become the major beneficiaries of Nader's efforts.

"A lot of the big companies are ridding in on big DOE (Department of Energy) contracts," Nader says, suggesting that once the solar energy industry is at peak development it could replicate the auto or steel industry. If that happens, Nader asks, "How are we going to decouple from central corporate distribution."

Already, some of the small, innovative companies that Nader hoped would develop are being brought up by the giants, particularly in the field of photovoltaic cells, which convert sunlight into electricity.

Atlantic Richfield bought Solar Technology International now Arco Solar. Mobil Oil bought Tyco Laboratories, now Mobil Tyre. And Shell Oil is the major stockholder now in Solar Energy Systems. Others, such as Exxon and Motorola, have preferred to build up their own companies.

Anthony Clifford, an executive with the largest remaining independent solar cell company. Solarex, says, "We have been approached by numerous Fortune 500 companies, including several major oil companies."

Some solar advocates say this is necessary to press the development and commerialization of technologies at this point which remain capital intensive. A recent DOE study completed by the Jet Propulsion Laboratory concludes that the oil companies and the so-called "systems" companies such as the largest aerospace firms are in the best position because of their financial staying power and management.

The fact that corporate America has joined the environmentalists and consumer advocates in backing solar power is seen by DOE Application Omi Walden as a positive sign. "It means that solar has a truly national constituency, which is what is needed if we are to develop it," Walden says.

Obviously, corporate America foresees big profits down the road. "Ten years from now, the solar industry will be a big business," says Sheldon Butt, president of the Solar Energy Industries Association.

At the moment, however, solar power remains largely uneconomic and dependent on subsidies. Still, its promise is such that it has a nearly unstoppable following on Capitol Hill.

"Nobody is antisolar in Washington in a political sense," says Denis Hayes, head of a national solar lobby coalition and an originator of Sun Day.

A recent Harris Survey found 94 percent of respondents in favor of solar energy development.

This popularity is not lost on the Congress.

Last week the Senate approved a House-passed bill under which the government would buy $1.5 billion worth of photovoltaic cells over 10 years - a big shot in the arm for companies such as Solarex, Westinghouse, and Arco Solar.

The Senate also passed a measure that could waive the 4 cents a gallon federal motor fuel tax on gasabal, a mix of gasoline and alcohol. Gasohol can be made from grain, wood chips, sugar, even cheese. Many big grain companies, Holly Sugar, and Archer Daniel Midland, the nation's largest corn sweetner producer, and Standard Bread's which makes gin, are major backers of the measure.

There are also tens of millions of dollars in tax credits in the Carter energy plan for homeowners and commercial building owners who install solar equipment.Congressional analysts any these credits will spur as much as $1.5 million in new sales yearly until the credit runs out in 1985. The beneficiaries of the credit would be the major heating and cooling manufacturers, including Grumman, General Motors, Aluminium Co. of America, General Electric and the metals giant, Asaroa.

One of the most heavily lobbied solar projects that failed in Congress this year was the solar power satellite, called Sunsat by its backers. The satellite system would cost up to $60 billion and, for obvious reasons, was pushed by the aerospace industry, including companies such as Boeing, Martin Marletta, Westinghouse and General Electric. They wanted Congress to approve a $25 million evaluation study for DOE that would have provided the opening for a program that could lead to a test launching in the next decade.

Solar has also joined the lists of most-sought-after projects a House member or senator can win for a district.

Before his death Sen. John J. McCellan (D-Ark.) artfully steered appropriations through both houses for a major solar demonstration program at Blythville, for the Mississippi County College. "It is common knowledge that McClelland took the baon hope on that one," says one DOE official.