A massive cloud-seeding program aimed at coaxing a few inches of rain from California's infrequent summer storms will be launched Wednesday with few illusions of success.

"There's no pretense about this," said James Welsh, chief of the California Department of Water Resources' planning branch. "We're doing it on the come. There's no guarantee of anything, but it's a chance worth taking."

The agency's willingness to gamble reflects the realities of the severe drought that followed the driest winter in California's recorded history. While various water conservation measures will pull the state through the summer, some reservoirs containing water needed for California's $2.6-billion-a-year agricultural economy are certain to go dry if the rainfall and snowpack this winter fall significantly below normal.

Welsh said that the Department of Water Resources is operating on the basis of forecasts that call for the 1977-78 winter to be a repetition of last year's, when statewide water runoff was 25 per cent of normal.

If there are any clouds in the sky, the department will send up three twin-engine cloud-seeding planes Wednesday over a 40,000-square-mile mountainous area extending from the Kern River near Bakersfield to the Oregon border 550 miles north. The planes will search for cumulus clouds in an area where the summer rainfall in normal years averages only one-half inch to four inches.

The three planes, which will seed clouds for two months, are the vanguard of a huge assault that will be made on storms in the late fall and winter by a variety of federal, state and local agencies and private utilities. Welsh estimated that the total effort would cost $750,000.

This does not include the cost of a long-term weather modification study by the U.S. Bureau of Reclamation, which is setting up shop in Auburn, Calif., in the foothills of the Sierra Nevadas. The bureau's $11 million program, known as the Sierra Cooperative Pilot Project, will try to increase the winter snowfall over the entire American River basin, where the runoff would flow into Folsom Dam near Sacramento.

The summer cloud seeding has the more modest goal of reducing fire danger, increasing moisture for rangeland and increasing the soil moisture base for next year's snowpack. Snow that falls on wet soil produces considerably more runoff than snow that falls on dry ground.

As an indication of the difficulty of producing summer rainfall in California, the Department of Water Resources will count the cloud seeding a success if it produces one to two inches of rain.

Cloud seeders, operating either from planes or ground-based generators, hurl silver iodide crystals into storm clouds. There is disagreement among scientists on the success of cloud seeding, but it is generally accepted that at least modest increases of precipitation can be obtained from the process.

One utility company, which has been seeding clouds for 27 years near Lake Almanor in northeastern California, estimates that water runoff from the snowpack there has increased 6 per cent annually. This seeding has been done in the winter, when cumulus clouds occur frequently. They are rare finds for cloud-seeding pilots in the summer.

In addition to the problem of finding the right clouds, public agencies have held back from summer seedings for fear they would provoke the wrath of vacationers who might be drenched while hiking in the mountains. This concern is of minimal importance now.

While California is seeding clouds officials in other western states are looking to the federal government.

George Lamb, who is coordinating Colorado's drought-fighting efforts told a water symposium in Denver last week that the state has worked out plans with the Army Corp of Engineers to send in Army tank trucks and storage tanks if they are needed later in the summer. The water-filled trucks and tanks also would be available for use in Wyoming and other western states, according to Army officials.