Home mortgage interest rates in the Washington area have soared past 12 percent, propelled by the Federal Reserve Board's decision to restrict credit as a way of fighting inflation.

Mortgage rates jumped about one-quarter percentage point in the past week and have gone up nearly a full point in the past month, according to two firms that specialize in gathering data on home financing.

This week's quarter-point increase in interest rates added about $37 to the monthly payment on a $100,000 30-year mortgage and more than $13,00 to the amount the buyer will pay over the life of the mortgage.

The one percent increase in the past month tacked nearly $150 a month onto the mortgage payment of $100,000 loan, pushing the monthly bill to about $1,064 and adding $53,000 to the total housing cost over 30 years.

For home buyers willing and able to pay those rates, mortgage money is still available, but a handful of local lenders dropped out of the mortgage business this week and more are expected to do so by the end of the year.

The skyrocketing mortgage rates put intense pressure on the Federal Housing Authority and the Veterans Administration to raise the maximum rate on FHA and VA mortgages.

The ceiling on those government-guaranteed loans is 10.5 percent. At those rates, the only way an FHA or VA mortgage can be obtained is for the seller to take a substantial discount on his asking price and pay the money to the lender in the form of "points." One point is one percent of the selling price.

As of this week, the FHA/VA discount demanded by lenders jumped to between 7 to 10 points, so much that most home sellers will not participate in the programs.

The FHA and VA yesterday reportedly were considering jumping their interest rates by as much as a full percentage point to 11.5 percent. The FHA/VA rate hit 10.5 percent less than a month ago.

The latest details on the mortgage situation in the Washington area were obtained from Interest Data Reports, published by Bictor Peeke & Associates and Builders, Bankers & Realtors, edited by Walter Preston. The two rival services survey virtually all local mortgage lenders and publish detailed reports each week.

Preston said his reports on Maryland lenders showed that mortgage rates moved up as much as one percent this week, but the average was about one-quarter point. "By next Thursday, it might well be up another quarter to a half," he predicted.

The two surveys showed that quoted mortgage rates varied widely, from as low as 10.5 percent from one small Eastern Shore savings institution to 16 percent from one private Baltimore mortgage lender, who admitted he expected no business.

Generally the surveys showed rates average about 12 percent for the standard 20-percent-down mortgage, about 12 1/4 percent with 10 percent down and 12 1/2 or higher for 5 percent down.

Maryland National Bank, the largest lender in the state, raised its rate one percentage point, to 12 percent on 80 percent loans, and Loyola Federal Savings and Loan raised rates by between 5/8 and 7/8 point.

More than 40 percent of the Maryland lending institutions are out of the mortgage market, and that number is heading toward 50 percent, preston said.

But peeke said his areawide survey indicated only half a dozen lenders dropped out in the past week.

Nationally mortgage money is expected to dry up completely in 24 states which have usuary laws limiting mortgage interst rate to 12 percent or less.

Neither Maryland nor Virginia have limits on mortgage rates, and District of Columbia Major Marion Barry signed a measure last week temporarily raising the ceiling in the District from 12 percent to 15 percent. That limit will remain in effect for three months, unless the city council extends it further.

The District's 15 percent limit appears to allow mortgages to go as high as the highest preditions emanating from mortgage industry sources.

Jay Janis, chairman of the Federal Home Loan Bank Board -- the agency that regulates and finances savings and loan associations -- predicts that mortgage rates will keep climbing until they hit 14 percent.

Janis estimated that the number of new houses built will fall between 20 and 25 percent, warning that "1980 will not be a good year for housing, nor will it be a good year for savings and loans." By 1981, new home construction should return to normal levels, he said.

For the time being, new homes may be easier to buy than older ones because many home builders already have arranged mortgage financing for the houses they are building. Many savings and loan associations also have reserved funds for lending, which will enable them to keep making loans.

Because other investments can pay savers higher interest rates than savings accounts, savings and loan associations are getting few new deposits to use for mortgage loans. Instead they are raising money through what is known as the secondary mortgage market, by selling groups of mortgages to investors.