New gasoline taxes and federal grants are helping stop further deterioration of the Washington area's crumbling roads and bridges, but highway engineers say they have nowhere near the money needed to clear up a tremendous backlog of repair projects.

The potholes, rusty girders and steel plates that seem to deface everything from the Capital Beltway to the back alleys of the District of Columbia are telling evidence that road maintenance has been short-changed for years here, as in other financially pressed cities around the United States.

But Washington area lawmakers have begun to rethink that approach. The Maryland and Virginia legislatures this year took the politically painful step of raising gasoline taxes and other highway user fees. Renewed efforts were launched in Congress to get money for D.C. roads and other highway projects.

Today, highway crews are carrying out major repair jobs that not long ago would have died for lack of funds--or concern.

The pock-marked Woodrow Wilson Bridge is about to get a new deck at a price of $24 million. D.C. is pursuing plans to rebuild at least 30 miles of roadway a year. Sections of the battered Beltway in Prince George's County are to get a new asphalt surface.

With President Reagan and major congressional leaders having endorsed an increase in the federal gasoline tax equivalent to 5 cents a gallon, which would yield about $4.4 billion a year for highways, area officials are hoping that they might speed their fix-up programs further.

The less heavily traveled county systems continue to face a pinch, however. Depending on property taxes for much of their road costs, county revenues continue to be outpaced by increases in asphalt and construction prices. Engineers there find their budgets buy a bit less each year.

D.C.'s roads may well take the prize as the area's worst. After canceling some $2 billion in interstate highways in the early 1970s, the city began diverting most of the money to Metrorail construction. Routine maintenance on the city's 1,000-mile grid of streets was neglected.

By the late 1970s, with potholes breaking out in epidemic numbers, the city was forced to act. It decided to save the last $150 million from the canceled highways to refurbish existing roads and bridges and to reject Metro's requests for some or all of that money.

The basic annual target is reconstruction -- replacement down to foundations, as opposed to new asphalt toppings--of 30 to 35 miles of roads and one or two big bridges. (This work is separate from the city's highly-publicized program this summer to recoat residential streets.)

If that pace is maintained, "each street would be done on an average of every 30 years," said Wallace Cohen, a programming officer for the city's Department of Transportation. The goal is to prevent further deterioration, Cohen says. "It's not a catch-up program."

This past summer, the city began preparations for rebuilding the streets around the Convention Center and 16th Street N.W. between Alaska Avenue to Emerson Street, among other projects. It began taking bids for a contractor to rebuild the bridge that takes Franklin Street NE over rail track between 8th and 9th Streets NE.

Projects planned for next year include major work on the crowded Southwest Freeway between South Capitol Street and the Washington Channel, at a cost of $3 million to $5 million. Work may begin also on redecking the outbound span of the 14th Street bridge.

D.C.'s plans are hostage to Congress, which must appropriate the dollars on a year-by-year basis, and last year forced considerable cutbacks. Maryland and Virginia, in contrast, have raised state fuel and highway taxes to generate the needed revenues. In both states, however, the increases were well below levels highway officials said were needed.

Proceeds from the nine-cent-per-gallon pump tax enacted in Maryland in 1972 peaked in fiscal 1979 at $200 million and then began to decline, as motorists switched to more fuel-efficient cars. After heavy lobbying from Gov. Harry Hughes, the legislature earlier this year passed a compromise package to raise the tax two cents this year and another 2 l/2 cents next year.

Eugene Camponeschi, chief state highway engineer for Montgomery and Prince George's Counties, says the new tax has enabled him to move up many improvement and repair projects. Among the major ones:

Resurfacing of the Beltway between Rte. 50 and Rte. 214. Work on that job, expected to cost about $2.7 million, is expected to begin next spring.

Conversion of Rte. 198 (Ft. Meade Road) between U.S. Rte. 1 and the Anne Arundel County line to a four-lane divided highway. The $9.5-million project includes two new bridges.

Widening and redecking the bridge that carries Montrose Road over I-270, expected to start in late 1983 and cost about $1.2 million.

The Maryland State Highway Administration is also overseeing the redecking of the Woodrow Wilson Bridge, one of the area's busiest arteries, using funds specially provided by Congress. Construction, which will limit traffic to one lane each way at night, was to begin last week but was put off due to materials problems.

In Virginia, state highway officials have received a welcome increase in funds from a tax increase approved by the legislature. State highway officials had warned that no rise would mean stopping all construction and reconstruction in 1984 and devoting all funds to resurfacing and other routine maintenance.

The legislature imposed a 3 percent wholesale tax on gasoline, as well as raising vehicle registration and licensing fees.

With the price of gasoline down nationwide, the tax is bringing in less than was hoped for. Still, state highway official David Gehr says the new tax probably made the difference between proceeding with many high-cost projects in Northern Virginia and canceling them. They include:

A new $3.4-million bridge to carry northbound Rte. 1 traffic over the Occoquan River. (The old bridge was taken down several years ago.)

Widening Rte. 123 from near Braddock Road to south of the Southern Railway crossing from two to four lanes.

Adding a lane on both sides of Rte. 7 in the Tysons Corner area, at a cost of about $700,000.

Improvements to the interchanges where I-66 crosses Rte. 50 and Rte. 28.

The suburban counties, which generally maintain the area's less busy residential streets, are also facing cost squeeze, though their officials feel their roads are in better-than-average condition for the area.

The $2-million maintenance budget for Arlington County's 376-mile system is expected to rise only 6 percent next year, which road operations chief Dennis Johnson says will not quite cover the rise in inflation.

In Prince George's County, the Bureau of Roads and Bridges budget rose only 3 percent to $6.43 million this year. Montgomery County, meanwhile, has reduced its maintenance staff and switched from an 8-9 year resurfacing cycle to 10 years in a bid to save money.