Residential building permits in metropolitan Washington, which suffered an unusually frigid siege, totaled 938 in January, a 45 per cent drop from the 1,720 permits filed in December.

Figures compiled from 12 area political subdivisions by the economics department of the National Association of Home Builders, also showed that all but 28 of permits were for single-family dwellings and townhouses intended for the sale market. All the milti-family permits were in the Distric.

A year ago, when housing was just beginning to emerge from a slump, area-wide permits in January totaled 1,020. In January, 1975, only 332 permits were filed.

The only significant increase in recent area permits was in Fairfax Country, where the January total was 347 against 234 in that month in 1976. Generally, Fairfax has been the most active home building county in this area in recent years.

Michael Sumichrast, chief economist of NAHB, said that the total of residental permits filed in 1976 was 17,626 units. The breakdown included 13,335 single houses, up 82 per cent from the 7,315 permits in 1975 - the lowest figure on record.

In 1976, multi-family permits covered 4,291 units in this area, up 77 per cent from the 2,444 total in 1975. The current area forecast for 1977 anticipates 14,500 single-family starts and 5,200 multi-family units.

On a national basis, the NAHB forecast is 1.8 million dwellings to be started this year, up from the 1.54 million residences started in 1976. That latter figure represented an increase of 32 per cent above the 1.16 million total in 1975, the lowest in 30 years.

While the area and national outlook for new housing is brighter this year, the main health of the industry is concentrated in southern California and in Houston and Dallas. However, builders in Florida and some sections of the Northeast are not nearly as activr.

One factor that indicates a strong year for both new housing sales and resales of existing dwellings stems from the strong supply of conventional mortgage funds available from savings and loan associations. Their basic lending rates now range between 8 1/2 and 8 3/4 per cent. And there has been pressure on the Federal Home Loan Bank Board, which regulates those private associations, to encourage even lower rates. The current FHA-VA rate ceiling now is 8 per cent and it is expected to remain at that level, despite some talk about a slightly lower ceiling.