The recent sharp rise in interest rates has increased the popularity of adjustable-rate mortgages while putting the brakes on mortgage refinancings, according to a survey by the Mortgage Bankers Assn. of America. Interest on 30-year, fixed-rate mortgages averaged 10.47% in early May, compared to 9.12% in early March. Meanwhile, rates on the initial year of one-year ARMs declined to about 7.74% in early May from 8.2% in October. The group's survey of 20 major mortgage lenders indicated that during the period, the percentage of buyers choosing 30-year fixed mortgages fell to about 62% from 79%, while the number of buyers choosing ARMs jumped to 18.5% from about 9%.