Departing from past assessments, congressional researchers said this week that solar energy must be taken seriously as a source of electricity as well as heat for individual homes, apartment buildings and offices.

The report by Congress' Office of Technology Assessment said small devices supplying electricity, heat and hot water for a single building offer an important - but often ignored - rees of energy.

The two-volume report, described as the most exhaustive analysis to date of small-scale solar devices, differed sharply from past government studies that discounted the promise of solar electric generation for individual homes.

It said federal research programs so far have slighted development of home-size solar electric generators and have overemphasized big, centralized solar stations comparable to conventional utility power plants.

urging reversal of the trend toward centralization, the office said the sun potentially can provide economical total heating for apartments in 5 to 10 years and partial home generation of electricity within one or two decades.

The report called for more emphasis on small, onsite solar electric systems and suggested major revisions in administration energy policies - including incentives for manufacturers, prizes of $50,000 to $100,000 for inventors and tax breaks of users - to boost all types of solar development.

Without federal help, the report said, solar power will grow very slowly from its present role of supplying less than one-thousandth of 1 per cent of the nation's total energy. It said the growth of solar power also depends on increased prices for other energy sources.

OTA analysts examined four cities - Albuquerque, Omaha, Boston and Fort Worth - where extensive sunlight measurements have been made.

In all but Omaha, they said, it should be possible by 1980 to use 100 per cent solar heating and hot water in large buildings at costs comparable to electric heat - providing that electric rates go up 40 per cent. They said total solar heating would be competitive inment tax credit.

Within a decade, the report said, it may be possible to generate electricity in home-size units for prices

While a recent test by the New England Electric System and Arthur D. Little, Inc., the first on a large scale for homes in use, showed that solar water heating systems saved only 17 per cent in energy costs, one HUD official dismissed the results as based on out-of-date technology.

"It's like pitting the Wright brothers against the SST," said Joseph Sherman, director of building technology and standards research for the housing agency, in an interview. He said a whole generation of solar development has passed since the water heaters in the New England experiment were installed two or more years ago. Solar water heating is now a "sophisticated industry," he declared.

Technical standards recently issued by HUD will not require manufacturers to achieve a given efficiency rate in the same way government standards now set automobile mileage efficiency, he said. Nor will efficiency labeling be required, as it is for certain appliances, he added.

The state of the art has not yet advanced to that point, Sherman said, but it has advanced beyond that indicated by the New England test, which surveyed 100 houses in Massachusetts, New Hampshire and Rhode Island.

Half of the solar heating units experienced mal-functions such as faulty wiring and pipe leaks. John R. Stevens, vice president of the New England utility company, said he believed inadequate design was responsible. The systems will be retested in two years to see if corrections improve the operating efficiency.

Meanwhile, several small solar-heating contractors in the Washington area have reportedly gone out of business in recent months, the victims, one contractor said, of delays in approving tax credit incentives for installing solar systems.

Home owner interest in solar heating intensidied over the cold winter, said John McCombs, the former owner of a solar systems company, but business for such firms has fallen off sharply while the federal debate over tax incentives continues. Large, diversified companies can wait this out with greater ease, but small firms are being "starved out," McCombs said.