Foreclosures on homes reached post-Depression highs in the first quarter of this year, the Mortgage Bankers Association reported yesterday, in a vivid sign of the length and depth of the current recession.

The number of homeowners who have defaulted on their mortgage payments also rose to new highs, running parallel with soaring unemployment rates.

The foreclosure rate rose from 0.44 percent of all mortgages during the first quarter of 1981 to 0.53 percent this year--meaning that about 100,000 homes were in the process of foreclosure. Defaults of more than 30 days rose from 5.28 percent in last year's first quarter to 5.35 percent this year. By comparison, the delinquency rate was 3.41 percent for the same period in 1972, and the foreclosure rate was 0.22 percent.

The dismal figures also are likely to get worse, the MBA said. This is because unemployment and interest rates continued to rise in the quarter and are not expected to decline sharply any time soon. Trends in delinquency and foreclosure rates generally lag behind those economic indicators.

Mortgage payments traditionally are the last debt that homeowners default on, because they want to protect what for many is the largest investment they ever make.

In addition, banks and S&Ls usually have avoided foreclosing on homeowners--even when they are far behind in their payments--because lenders are not equipped to handle real estate and do not want to have to manage or sell it.

The foreclosure rate, therefore, is an indication of how serious the unemployment and delinquency problems have become nationwide.

"If the lender can see an end to the problem in the next year or so, it might string along with" the defaulting homeowner, said MBA Executive Vice President Mark Riedy. But new record highs in delinquencies of more than 60 and 90 days are particularly disheartening, because they show a longer-term problem that lenders are having to deal with, he said.

Although long-term unemployment has forced more people into default than ever before, high interest rates have made it more difficult than in the past for families to sell their homes to pay off their mortgages when they get into financial trouble.

"Today you can't sell your house. You are just boxed in," Riedy said. Because prices have stayed flat, people would have to take a loss on their home to sell it at today's high interest rates, he added.

By far the highest delinquency and foreclosure rates were in the Midwestern states that have been hit the hardest by unemployment in the auto and construction industries. Illinois had the highest rate of defaults in the country, 8.12 percent of mortgages there; Ohio had the greatest rate of foreclosures, 1.33 percent.

The percentage of delinquencies in the Washington area generally was slightly lower than a year ago, but the percentage of mortgages in foreclosure was somewhat higher. In the District, the delinquency rate declined from 6.86 percent a year ago to 6.45 percent in the first quarter of this year, but the foreclosure rate rose from 0.80 percent to 0.89 percent. In Maryland, the foreclosure rate jumped from 0.25 percent last year to 0.35 percent this year; in Virginia the rate increased from 0.15 percent to 0.20 percent over the year.

The delinquency problem has caught the attention of Congress, and Democrats in both houses have proposed legislation to provide loans to homeowners facing foreclosure because they have lost their jobs. The House Banking Committee has approved the program as part of its housing authorization bill, but the proposal was defeated in the Senate.