A massive shift from oil and coal use to solar energy would create almost 3 million new jobs and cut spending for conventional fuels nearly $120 billion by 1990, according to a congressional study released yesterday.

Disputing previous estimates of major economic dislocation, the study called for creation of a new cadre of energy specialists to install conservation and solar energy equipment.

Such a boon to the U.S. economy is unlikely, however, unless the federal government establishes mandatory conservation standards for industries and private residences the study concluded.

The study was done for a Joint Economic subcommittee by researcher Leonard S. Rodberg, director of the Community Energy Project in Washington and a visiting scholar at Columbia University.

Critics of solar heaters and coolers as replacements for furnaces and air conditioners have said if coal, oil and natural gas consumption were substantially reduced, large numbers of persons would be out of work.

Rodberg estimates spending on non-renewable fuels could be reduced by $118.8 billion in 1990 if solar equipment is installed on a large scale and Americans invest in a wide range of conservation equipment.He also estimated there would be a net gain of about 3 million jobs:

Some 1.7 million new positions would be created for persons installing solar heaters and coolers.

Another half million persons would be hired for installation of insulation and other energy saving equipment.

Money no longer needed for fuel costs or utility bills would generate another 1.9 million jobs, the study said.

At the same time, about 1.1 million jobs would be lost in the oil, coal and natural gas industries, the study said.

But the study noted that neither utilities nor oil companies have shown much interest in marketing solar heating and cooling units.