District budget officials have slashed nearly one-third of the city's funding for the "War on Rats" in fiscal 1983 because experts say that although the fight is not over, the rats no longer are winning.

The cut means 15,000 fewer homes and lots will be inspected for rodents in this fiscal year (which began October 1) and 4,000 fewer sites found to be infested will be treated, said James E. Murphy, chief of the city's bureau of community hygiene.

William B. Johnson, director of the city's Department of Environmental Services, said funding for the program will drop from $492,000 in fiscal 1982 to $341,000 this fiscal year, a decrease of about 31 percent. The District received more than $1 million when the program began, and funding peaked in fiscal 1970 at $1.2 million.

District officials acknowledge that there is still a mouse problem as well in the city, but contend that it is "not growing." City inspectors and rodent control specialists will help control only mice affecting indigents, invalids and welfare recipients. Other residents must do it themselves, although the office of community hygiene will offer advice.

The "War on Rats" budget has been reduced for several reasons. When the Reagan administration created a preventive health services block grant to replace direct grants to fund programs like rat control, it left the distribution of funds for a number of programs up to District, rather than federal, officials. In the process of changing how rat control and other programs are funded, the administration slashed the amount of money available from the Department of Health and Human Service's Public Health Service. Also, city officials believe they are winning the fight against rats.

"Our priorities in using the block grant money were combating VD (venereal disease) and tuberculosis," Johnson explained. "And armed with the improved means of containing garbage in the city called Supercan, we feel we can more than offset any decline in funding."

Supercans are mobile 85-gallon refuse carts with sturdy, sealable lids. The cans prevent dogs, cats and rats from getting into the garbage and allow the city to have its huge garbage trucks make only one pickup a week in seven of the city's eight wards.

Currently, the city uses Supercans for 70,000 of the 98,000 residences that depend on city trash collection. The cans are impractical in some parts of the inner-city area, where trucks can't navigate between cans in narrow alleys. Parts of Ward 2, which includes Georgetown and the embassy area along Massachusetts Avenue, also do not have Supercans because of narrow alleyways.

"Supercans are the best thing since sliced bread in terms of rat control," Johnson said. "With this improved system of collecting garbage we have already offset any potential increase in rodent infestation that could be attributed to the budget cut."

Johnson emphasized that city rodent control inspectors would concentrate on the areas without Supercans.

"For $36 a can, it costs much less to buy a Supercan than it does to keep rats under control using poison ," Johnson said. "And the cans allow a better appearance in the neighborhood because you don't have blowing litter."

"When we started the program in 1969, in some areas of the city rodent infestation was up to 48 percent," Johnson testified last summer at a House Appropriations subcommittee hearing on the city's budget. "We have something like a 6 percent level city-wide at this moment, which is a very respectable reduction."

The "War on Rats" program was created by Congress in the late '60s in response to the urban riots. Legislators were trying to respond to the need to clean up urban slums.

At that time, Mayor Marion Barry was director of operations for Pride Inc., a community action group that was at the forefront of trying to eliminate rats from the city's slums.

"The major problem we still have is in the inner-city area where people don't always use approved containers for on-site storage of refuse," Johnson said.

Murphy, who has been involved in the rat control program for more than a dozen years, attributes the success in reducing rat populations to the "knowledge, skills and techniques" the city uses against rodents, such as switching from warfarin -- a rodenticide to which many rats had become immune -- to a "backyard blend" of several different chemicals that city workers mix up, regularly changing the proportions.