The People's Savings Bank of Bridgeport, Conn., has stopped making out-of-state home mortgage loans.

While the policy change will have negligible impact on the nation's housing market, it is indicative of the bank's concern over the trend of sharply reduced net new deposits for thrift institutions in recent months. In some cases, savings outflows have grown to exceed inflows.

This concern now is widespread among savings institutions, which recall only too well the massive withdrawals of 1973-74. In those years, loss of deposit dollars left the thrift industy with insufficient funds to meet loan demands - and this sent mortgages rates sky high.

Such a scenario is not expected for 1978, but the memory is fresh enough to make savings institutions like People's Savings Bank more careful this time around.

Indeed, Wright Investors' Service, an investment management firm, warned in recent newsletter that new 90-day Treasury bills are already up to the "level which triggered savings outflows . . . in 1973."

The thrift industry, however, contends that it is better prepared than ever before to cope with the adverse conditions it faces.

The recent decline in new net deposits stems from rising short-term interest rates, which began moving up dramatically in the fall of 1977. When these rates exceed the divided rates paid by savings institutions, some savers move their money to higher-paying instruments, such as U.S. Treasury securities.

Three-month Treasury bills recently have been paying about 6.4 percent, an attractive alternative to a 90-day 5.75 percent notice account at a savings and loan.

While it is difficult to know where withdrawn savings deposits end up, recent figures document the increasing severity of the outflow:

In December, the nation's mutual savings banks had an estimated net outflow of $75 million. A year earlier, the banks recorded a net increase in deposits of $367 million.

Savings and loan associations had deposit growth of $1 billion in December, less than half of the $2.4 billion increase of a year earlier.

This decline in savings growth is "likely to continue for several more months, and means some tightening in the supply of mortgage funds," noted Norman Strunk, executive vice-president of the United States League of Savings Associations.

So far, the savings outflow has not hampered the booming housing market. Housing starts in December of 1977 were at the highest level since March 1973, exceeding 2 million units for the sixth consecutive month.

But thrift institutions are watching their loan commitments carefully. "A typical move is limiting out-of-state lending," says George Hanc, senior vice-president and chief economist for the National Association of Mutual Savings Banks.