Washington — The recent rise in home mortgage rates will be a short-lived squall, not a hurricane blowing through the housing market, industry experts say. Upticks in the cost of both conventional and government-insured loans are likely to be ''a temporary aberration,'' says Larry Brean, vice-president of planning for Ryan Homes Inc., a major home builder based in Pittsburgh. ''We really don't see it having too much impact on our business.''
Of course even a minor mortgage rate cloudburst can spell bad news in the interest-sensitive housing industry, still recovering from the worst slump of the post-World War II period, a slump set off when mortgage rates started soaring in 1979.
''I don't think it will kill too many sales,'' says Treasury Secretary Donald Regan of last week's half percentage point rise in the cost of government-insured loans. ''But it gives the wrong signal to people. They get confused as to what the future is.''
The future holds the prospect of lower mortgage interest rates by the end of 1983, most housing observers say. If this financing forecast is correct, then the rebound in existing home sales and new home construction will continue into 1984, thus helping reduce the nation's unemployment rate.
''We expect mortgage rates to come down another 1 percent'' before the end of 1983, says Donald Straszheim, vice-president of Wharton Econometric Forecasting Associates.
Government-insured loans now carry a 12 percent rate. In May, conventional new-home loans carried an average rate, including miscellaneous fees and charges , of 12.64 percent, according to the most recent Federal Home Loan Bank Board data.
The cost of fixed-rate, conventional loans should ''move to the neighborhood of 11.5 to 12 percent by the end of the year,'' adds Rosemary Rinder, assistant vice-president and economist at New York's Citibank.
Interest rates have moved up as financial market participants worried about the Federal Reserve Board's ability to control the nation's money supply, which has been increasing rapidly.
''We believe that the recent increase in money growth is a short-term matter associated with (banks' new) money market accounts,'' Mr. Straszheim says. ''Money growth is going to ease substantially in the second half of the year of its own volition,'' he says, thus letting interest rates fall.
Unless the Federal Reserve ''in a heavy-handed way'' boosts the money supply further, ''we will see the recent run-up in rates rescinded,'' says Kenneth Kerin, vice-president for economics and research at the National Association of Realtors.
But until mortgage rates stop rising and start to fall, home sales may cool off. ''My expectation is that we will see an easing in the housing sales rate,'' Mr. Kerin says. ''We have run out of people who can afford homes at a 13 percent'' mortgage rate.
In April, existing homes were selling at a 2.75 million annual rate, up just 1.5 percent from the March pace. Sales of new homes also slowed in April, to an annual rate of 573,000, down from a 597,000 annual pace in March.
And the upward notch in interest rates is also expected to put a temporary damper on home prices. The median price of an existing home had been rising steadily since October, according to National Association of Realtors' data. But prices stood still in March from the April level, Mr. Kerin says, with the median sales price unchanged at $68,900.
''When (mortgage) rates go up, you pay more in interest. So (buyers) can afford less in the basic (home) price,'' he says.
The rise in mortgage rates has also contributed to a dampening of demand for new homes, according to Michael Sumichrast, chief economist of the National Association of Home Builders. ''I think we are seeing a slowdown in the (sales) activity.''
Mr. Sumichrast expects builders to start new homes at a somewhat slower rate during the second half of the year than during the first quarter, when homes were being started at better than a 1.6 million annual rate. But for 1983 as a whole he still expects starts of 1.55 million, a major improvement over the 1.06 milion pace last year.
''And if interest rates do soften, we are looking for 1.75 million starts in 1984,'' he says. Other forecasters expect an even faster pace of construction activity next year, with Wharton predicting starts of 1.86 million. That forecast is based on mortgage rates ''heading down a bit more,'' perhaps another full percentage point, Mr. Straszheim says.
Forecasting long-term interest rates is a risky business. But even if mortgage rates remain at current levels, housing activity should pick up in '84, says Ms. Rinder at Citibank. She predicts inflation-adjusted gross national product will rise by 3 or 4 percent next year. That would help the housing market by boosting personal income and cutting unemployment.