Consumer prices rose faster in the Washington area than they did nationally during December and January with a two-month jump of 2.9 percent.

It was the largest area increase since the federal government began keeping local statistics on a two-month basis at the start of 1978.

If consumer prices continue to rise at this pace for the rest of 1980, the local inflation rate would top 18 percent. However, most economists do not expect that to happen.

Steep increases in the costs of fuel and purchasing a home led the price rise, which was just above the national urban consumer price increase of 2.5 percent, the government's Bureau of Labor Statistics reported yesterday.

Gasoline prices rose here by almost 10 percent during December and January, compared with a 1.7 percent rise in gasoline prices at the pump during October and November. Nationwide, gasoline prices rose by 9 percent for the same recent period.

In addition, the cost of buying a home locally jumped by 6.4 percent during the two-month period ending in January, as interest rates hit record levels, compared with a 0.8 percent rise over the previous two months.

A government economist said that the average new mortgage payment increased by 13.9 percent locally during the recent two-month period, compared with a 3.8 percent increase during the previous two months.

In the Washington area, it is virtually impossible to get a new home mortgage now at less than a 13 percent interest rate.

(Area lenders have boosted home mortgage rates to 14 percent or more in the past week and housing money has become scarce. Stories on Pages D9, E1.)

Washington area prices in January were 11.1 percent higher than a year earlier, an increase lower than the national average increase of 13.9 percent.

Price increases here during the final months of 1979 trailed national averages, primarily because discount food retailers here added new competition to the grocery marketplace, keeping food prices down.

The metropolitan consumer price index stood at a record 231.9 at the end of January, which means that good and services that cost $100 in 1967 now cost $231.90. The national index last month was 233.2, up 1.4 percent from December.

The local figures are particularly startling because the two-month inflation rate in the metropolitan area had been well below the national average during late 1979. For the August-September and October-November periods the government said the consumer price increase for each was 1.1 percent.

Andrew Brimmer, a former member of the Federal Reserve Board and now the head of Brimmer and Co. In., said the consumer price data indicates "the high cost for mortgage interest rates for homes was substantial," but that overall, the metropolitan area's inflation rate "tracks the nation" in most goods and services.

Robert Tardio, chief executive officer of Suburban Bancorporation in Hyattsville, said that the reported inflation rate for the Washington area is low. "Food and other prices are up well in excess of 2.9 percent," Tardio said.

Tardio forecast that the nation and the Washington area will have an inflation rate this year well in excess of 11 percent, despite the Carter administration prediction that inflation for 1980 would be 10.4 percent. "That's a bunch of hogwash," said Tardio, who heads the Greater Washington Board of Trade business development bureau.

The signs of inflation in Washington became more apparent during late 1979. Although grocery prices dropped by 0.7 percent in October and November, food prices rose by 1.3 percent in December and January.

Prices for beef, pork, fish, seafood and eggs rose, the government reported. Overall, grocery store costs rose by 7.8 percent for the year ending Jan. 30.

On the other hand, medical costs in the Washington area rose by 1 percent during the recent two months, compared with a nationwide jump in medical costs of more than double that figure.

Further, the cost of apparel here dropped during December and January by 1.8 percent, although the increase for the year ending Jan. 30 was 12.1 percent.