A sampling of midsize life insurance companies shows most will not scale back their commercial real estate lending in 1991, despite the perception the economy is suffering from a credit crunch, according to a new survey released Friday.

The Mortgage Bankers Association of America survey of 36 midsize life insurance companies said 31 percent expect to increase their lending in 1991.Mortgage Bankers Association president James W. Nelson said medium-size life insurers have about 35 percent of all permanent commercial real estate loans held by the life insurance industry but typically are not involved in short-term lending.

"The so-called credit crunch which we read about, and believe me it is a reality, affects shorter term lenders for construction" such as commercial banks, Nelson said. The life insurers are more involved in longer term mortgage lending, he added.

Businesses, particularly in New England, have complained bank loans are drying up at a rapid pace as lenders work to boost their profitability in the recession. The resulting credit crunch threatens the financial viability of many businesses, analysts say.

The survey said 77 percent of the companies saw higher delinquency rates in 1990 than the previous year. The mid-sized insurers reported a delinquency rate of 1.91 percent, compared with a 3.3 percent rate for the industry in general.