Consumers have begun to slow down their borrowing, in part because they can no longer get credit at either the bank or the loan company.

A survey of Washington area financial institutions indicates that the same factors are at work squeezing a larger and larger number of would-be borrowers out of the credit market that have produced a nationwide slowdown in the growth of consumer credit.

Banks and finance companies are looking harder at debt to income ratios, employment experience and the purpose of the loan before handing over the money for some types of loans and not making any at all for other types.

In addition, bank credit cards -- so easy to come by in the past several years -- are being issued at a slower rate and the volume in residential mortgages has sharply declined.

For some families, the contraction in credit came to late, according to credit conselors. Caught between existing debt and the rising cost of necessities, those families are finding it increasingly harder to meet their monthly payments.

"They're showing up with much more debt for their incomes than in prior years, and it's harder to help them because the basic cost of living is going up so high," said Jerry Lareau, president of Consumer Credit Counseling Service in New York. He said counselors across the nation are seeing similar patterns.

Nationally, consumers added only $35.7 billion to outstanding installment credit in 1979, compared to $44.8 billion in new debt added in 1978. As the year wore on and interest rates increased, the rate of borrowing decreased.

The largest decline came in auto loans, down from $4.7 billion extended in the first quarter of 1979 to $1.7 billion in the last quarter. The biggest increase in borrowing was on gasoline credit cards which rose from $188 million in the first quarter to $455 million in the fourth quarter.

Consumer loans by commerical banks fell from $2.2 billion initially to $249 million later in the year as banks here and nationally began to tighten their credit requirements.

In a move indicative of the changes in lending patterns, Union Trust Bank of Maryland last week sent out a directive instructing officer to lend only to previous customers.

At some banks including Union First of Washington and Virginia National Bank, consumer loan volume has declined, while at others, including National Bank of Washington, volume has remained static.

Local banks have taken a variety of measures restricting loans, including increasing down payments required for loans on automobiles and other major items. In addition, bankers are changing the rule of thumb about what percentage of gross income debt should be.

In the past a liberal limit has been 40 to 50 percent of income and a conservative limit, 30 percent. One area banker said he is reducing the debt load limit by 10 to 15 percent. Another said debt for loan applicants is now limited to 20 percent of income, not including the loan applied for.

Area retailers said they have seen no significant changes in the way department store consumers are using credit. But stores here and elsewhere have found credit customers slightly slower to pay, opting more often to make a miniumum payment than to pay the account in full.

Although local retailers have not changed the terms under which they extend credit, at least one major national retail store chain, Dayton's of Minneapolis, had raised the amount of the miniumum payment required on its accounts.

Stores that depend on finance companies to extend credit for purchases have found that the loan companies are also drawing back from extending credit in some cases. Nationally finance company loans declined from $2.1 billion in the first quarter last year to $1.8 billion in the fourth.

"The finance companies themselves over the last few months have tightened up their credit procedures," said an official of George's Radio & Television C. Inc.George's takes applications for credit from customers and forwards them to credit companies. "What we've done is try to expand our program using various finance companies," said the store official. Because the companies vary in what restrictions they impose on extending credit, "we bounce them back and forth between companies and try to find any kind of credit we can," he said.