Home mortgage foreclosures hit their highest level since the mid-1960s in the first half of 1982, when roughly one of every 400 families lost their homes because they couldn't keep up the mortgage payments.

A total of 21,425 American households lost their homes during the first half of the year, Federal Home Loan Bank Board Chairman Richard T. Pratt testified yesterday at a congressional hearing on the rising rate of home mortgage foreclosures.

The foreclosures amounted to about 0.27 percent of all home mortgages--roughly 1 of every 400, Pratt told a congressional committee considering proposals for emergency mortgage relief to Americans in danger of losing their homes through foreclosure.

Mortgage delinquencies--loans that are behind in payments--also are up, according to bank board figures. About 2.18 percent of loans were 60 days or more in arrears at the end of December, while a year earlier the delinquency rate was 0.83 percent.

Although they termed these statistics alarming, Pratt and officials of other federal regulatory agencies said they do not favor emergency foreclosure legislation, arguing that economic recovery has begun and will be strong enough to cut down the foreclosure rates.

Pratt predicted 1.4 to 1.5 million new homes will be started during 1983.

Foreclosure rates, which increase in times of high unemployment and economic stress, "lag unemployment rates both going into and coming out of a recession. Thus, we anticipate that the economic recovery now under way will largely address the underlying cause of increasing foreclosures," Pratt said.

Rep. Henry B. Gonzalez (D-Tex.), chairman of the housing subcommittee who also chaired yesterday's hearings, disagreed, saying, "What we are seeing now is a steep increase in the foreclosure rate, because as the depression drags on, there are progressively greater numbers of people who simply cannot hang on any longer."

Banking Committee Chairman Rep. Fernand J. St Germain (D-R.I.) has proposed that the regulatory agencies provide emergency mortgage relief for homeowners threatened by foreclosure.

A "mortgage workout program" operated by the Federal Reserve System "would likely involve a relatively large increase in discount window credit . . . and undermine the Fed's ability to control growth in the money supply," said Preston Martin, vice chairman of the Fed. The Federal Deposit Insurance Corp. also "would strenuously object to a scheme to assist mortgage interest payments with funds from our insurance fund," said the corporation's director of research, Stanley C. Silverberg.

Most banks and thrift institutions already are foreclosing only as a last resort, after working with mortgage holders to give them more time to make payments, the witnesses said.