Washington — Consumers can look forward to further reductions in the interest rates they pay on loans for homes, cars, and other major purchases, bankers and economists say.
''There will continue to be a softening in rates,'' predicts William Henle, vice-president in charge of consumer credit at the San Francisco-based Bank of America. The bank is the nation's largest.
But the additional trimming of consumer loan charges will be modest and will not extend to credit card loans, forecasters say. One reason rates are expected to be sticky is that lenders are concerned that massive federal budget deficits will push up interest rates, and thus the cost of the money they lend.
''Over the next six to nine months, there will be another 1 percent or so decline'' in a variety of interest rates, including those on some consumer loans , forecasts Allen Sinai, senior vice-president of Data Resources Inc., a Lexington, Mass., economic forecasting company.
Similarly, Charles Schenck, senior vice-president in charge of personal loans at Manufacturers Hanover Trust Company in New York, says the possibility of a drop in consumer loan rates of about one full percentage point ''is very realistic.''
Nonetheless, if current forecasts are correct, interest rates, on an inflation-adjusted basis, will remain at historically high levels likely to dampen consumer spending. While interest rate forecasting is a notoriously unreliable art, by year's end:
* Mortgage rates should be around 12 percent on conventional, fixed-rate loans, Mr. Sinai says. The contract interest rate on such loans with a 10 percent down payment and a 25-year maturity is currently 13 percent, according to the Federal Home Loan Bank Board.
* Forty-eight-month car loans from commercial banks could cost about 13 percent, according to Sandra Shaber, senior economist at Chase Econometrics, a forecasting company. According to the latest Federal Reserve Board data, such loans now cost 14.81 percent.
* Credit card loan rates ''will be extraordinarily sticky,'' says Donald H. Straszheim, vice-president of Wharton Econometric Forecasting Associates, and will end the year near their latest reported level, 18.89 percent.
The cost of borrowing is a key factor in determining how vigorously demand will rebound for consumer goods. For example, sales soared 55.2 percent at General Motors Corporation in the first 10 days of April. Analysts say the surge was at least partly caused by the carmaker's chopping the interest rate on selected car loans by 2 percent from last year, down to 9.9 percent.
While loans from auto finance companies on selected cars are now in the single-digit range, most consumer borrowing carries rates perched in the mid to high teens. ''They are an obstacle to the purchase of durable goods like appliances and furniture,'' says economist Shaber.
Analysts say high credit costs have contributed to recent lackluster retail activity. In March, retail sales were up only 0.3 percent over February. And February's numbers were revised downward, posting a 1.2 percent decline from January.
Even though consumer rates have declined somewhat in the past year, ''they are still very high'' when looked at on an inflation-adjusted basis, Mrs. Shaber adds.
The true cost of a loan can only be determined by adjusting the interest rate for inflation. Economists disagree on the best method of doing this, but one approach is to deduct the expected inflation rate over the life of the loan from the interest rate being charged.
From 1978 through 1982, the real interest rate on home mortgages was about 5. 5 percent, according to Jack Carlson, executive vice-president and chief economist of the National Association of Realtors. By contrast, in the first three months of this year the real rate was 8.6 percent.
Lenders offer a variety of reasons that consumer interest rates have declined less than the prime rate, which serves as a benchmark for corporate borrowing costs. Since February 1982, the prime has plunged 6 percentage points, from 16.5 percent to 10.5 percent.
Meanwhile, the rate banks charge on 48-month car loans dipped 2.24 points, from 17.05 percent in February 1982 to 14.81 this February, according to the latest available Federal Reserve Board data.
Perhaps the most important reason for the balkiness in consumer rate changes, bankers say, is that lending to individuals is a sharply different business from lending to companies. Consumer loans carry ''high processing costs and losses are higher than on business loans,'' says Mr. Schenck at Manufacturers Hanover.
And changing the cost of borrowing for credit card customers is time consuming, and until recently it was severely hampered by state usury laws. As a result, many banks were losing money on their credit card operations.
''They have been through a period where they were losing money. Now they are starting to make money and they won't lower rates'' quickly, says Thomas Harter, senior vice-president and chief economist of the Mortgage Bankers Association of America. The administrative cost of a $200 to $300 credit card balance accounts for ''a substantial portion'' of the 21 percent rate now being charged on some credit card purchases, he adds.
In recent weeks money has flooded into banks and savings-and-loans. Taxpayers rushed to open individual retirement accounts, while savers were moving dollars from money market mutual funds into the new money market deposit accounts financial institutions have begun to offer.
This influx of funds, however, is not expected to have a major effect on consumer loan rates. Banks and thrifts are paying high interest rates to attract IRA money, explains Michael Wilson, associate economist at the US League of Savings Associations. And the rate paid on money market accounts ''will change, '' he notes.
There is little incentive to reduce consumer loan rates drastically, he concludes, ''when you have no idea what you will be paying on [deposits] from week to week.''