Homeowners are defaulting at a record rate on their mortgage payments, the Mortgage Bankers Association reported yesterday, a vivid sign of how severely the recession has hit parts of the country and how it is reaching into the middle-income brackets.

More than 1 in 20 mortgages nationally are in arrears, the association's survey showed. In the District the rate is higher, 1 in 14; in Maryland and Virginia the rates are below the national average.

The association predicted the mortgage delinquency rate would rise even further in the next few months because of rising unemployment.

For the third quarter of 1981, 5.33 percent of all mortgage loans nationwide were 30 days or more past due, the highest rate the association has recorded since it began taking its quarterly survey in 1953. By comparison, the delinquency rate in the last half of the 1970s hovered around 4.5 percent. It went above 5 percent for the first time since World War II in the second quarter of 1980, according to an association spokesman.

"The current recession, with its high unemployment, could exacerbate the delinquency problem in the new few months, especially in those regions with large numbers of laid-off workers," an association analysis said. "The nationwide scope of the economic downturn is apparent in the substantial increases in short-term delinquencies shown in all regions."

While all regions showed increases, by far the highest delinquency rates were in the Midwest, where there have been heavy layoffs by auto makers and in related industries. The overall figure for that region was 7.78 percent. For Illinois it was 9.14 percent, the highest in the nation. The association spokesman said this may reflect the near-shutdown of the construction equipment industry that is centered in Illinois.

The District's 7.52 percent delinquency rate for the third quarter was up from 6.05 percent the previous three months. In Maryland the rate was 4.14 percent, up from 3.56 percent, and in Virginia it was 3.85 percent, up from 3.48 percent.

Unemployment in the District is substantially higher than in the surrounding areas, and this is a major factor in the difference between delinquency rates in the city and those in Virginia and Maryland, the association said.

Foreclosures on delinquent mortgages declined nationwide in the last quarter but are likely to rise again because foreclosure rates lag delinquencies by a few months, the association indicated. Fewer foreclosures in the third quarter reflected last summer's slight improvement in employment and interest rates, the association said.

Delinquency rates traditionally are much lower on mortgages than on other types of loans--and foreclosure rates are minuscule--because people will try to protect the substantial investment they have in their homes even when they are forced to default on other debts.

In addition, mortgage lenders generally do not start foreclosure proceedings until the mortgage is at least 90 days delinquent, and even then most try to work out arrangements to help delinquent homeowners pay what they owe. This particularly applies at a time when it would be difficult for lenders to resell the homes to get back their money.