The devastated housing market will not improve much next year, more families will start doubling up and rental units will become virtually unavailable, housing experts said yesterday in predictions ranging from gloom to more gloom.

The panelists agreed in testimony before the House Banking subcommittee on housing and community development that interest rates are the culprit, but they offered few suggestions on improving the housing outlook other than bringing inflation under control.

Some criticized the Federal Reserve's tight-money policy as having severely exacerbated the interest rate climb, and faulted the administration for its proposed cutbacks in Federal Home Administration mortgage insurance programs.

Michael Sumichrast, chief economist of the National Association of Home Builders, predicted that housing starts would be only 1.06 million units, only about half the 1978 level, and that 1982 could be even worse.

Almost no additions are being made to rental housing, and even the record-low vacancy rates nationwide fail to show that the available apartments generally are substandard, he added.

"The rental market is so tight, it virtually doesn't exist anymore. It's frightening," Sumichrast said.

Henry Schechter, AFL-CIO housing director, said that many families have had to resort to unwelcome alternatives to renting or buying a conventional home.

"In millions of one-family homes, a second unit is being carved out, often in basement or attic space. There are large increases in the number of families living doubled up with others in a single unit, and there has been a significant increase in the use of smaller mobile homes," he said.

Schechter said that a recommendation by the President's Commission on Housing to replace the current Section 8 and Section 202 low-income housing construction programs with direct rental subsidies to tenants would be "hunting licenses in short-supply markets that would add to inflationary pressure.

"Housing production and supply is likely to get worse instead of better," Schechter predicted. Citing the downward trend in housing starts, he added, "This trend is likely to be prolonged until the continuation of current monetary and fiscal policies deepens the economic recession to a level at which long-term funds for housing and business are not in much demand."

He called for credit controls to channel credit to productive purposes such as housing and away from uses such as corporate takeovers, commodity speculation and production of luxury goods.

Thomas Harter, chief economist of the Mortgage Bankers Association, also blamed the Fed's tight-money philosophy for the depressed state of the housing market and called the FHA home insurance programs "the backbone of the mortgage market" that have allowed millions of Americans to buy homes.

Harter predicted that a decline in interest rates will start to become obvious in the second quarter of 1982, and that mortgage interest will be at about 13 percent to 14 percent by June. That view was more optimistic than some of the others.

Peter Treadway, chief economist at the Federal National Mortgage Association, said the immediate outlook is for a "further worsening of conditions n the housing market as the latest round of interest rate increases works its way through."

Treadway said that he does not expect significant declines in long-term interest rates over the next five quarters, and that future housing activity will have to depend on a decline in short- to intermediate-term rates and wider acceptance of adjustable-rate mortgages.