The outbreak of rabies among certain animals in Northern Virginia and Montgomery County--thought to be the worst in the nation in recent years--appears to be intensifying and spreading into new areas around the nation's capital, health officials said.

Prince George's County recently reported its first case in decades; the District of Columbia has now had six cases in the past three months, the first in memory of local officials, and Montgomery has had at least 13 cases alone since Wednesday, with 119 confirmed in the past four months.

Health officials report rabid animals being found in most jurisdictions around Washington at much higher rates than last year.

Many jurisdictions are not testing all the dead animals found but only those that have had physical contact with pets or humans, and the number of wild animals with rabies in the Washington area is thought to be higher than reported figures indicate.

Rabies tests cost more than $450 per animal.

Jeff Lake, staff epidemiologist with the Virginia State Health Department, called Northern Virginia's rabies outbreak, which began last summer, "probably the most intensive outbreak in the nation and the only large one in proximity to a high-density population."

The Northern Virginia outbreak is suspected by health officials to have been caused by raccoons imported by hunting clubs from Southern states such as Florida, Georgia and North Carolina, where the disease is well established.

However, while health officials warn against contact with wild animals and of the need for rabies vaccinations for cats and dogs, they also note that human deaths from rabies--once an almost invariably fatal disease--are rare today.

The last rabies death in Virginia occurred in 1953, Lake said.

The District's chief of disease control, Ingrid Newkirk, said rabies vaccine shots for humans are much better now "and there's no excuse for anybody dying of rabies in 1983" if they are cautious about wild animals and have their pets vaccinated.

The vast majority of rabid animals found around Washington are raccoons, although rabid skunks, foxes, groundhogs, beavers and bats have been found and dozens of pets, mostly cats and dogs, have contracted the viral disease through contact with diseased wild animals. The list of afflicted animals includes a pet ferret, a cow and a calf.

Alexandria is the only large municipality that has yet to report a case of rabies and the only one that does not require vaccination of pet cats as well as dogs, although the City Council will consider cat vaccination legislation this week.

In 1982, Virginia reported more rabies cases than any other state except Texas--745 cases compared to 785 in Texas, with 92 percent of the Virginia cases occurring in the Washington suburbs, primarily Loudoun and Fairfax counties, said state health officials.

Last year, Fairfax had 292 rabies cases. So far in 1983, Fairfax has had 41 confirmed cases, compared to one case last year at this time, with 34 of the new cases inside the Beltway, said assistant county health director Dr. Garth Dettinger. "But that's because we're not really testing outside the Beltway since we know we have rabies there," he said.

The county tests all cases in which an animal suspected of being rabid is believed to have had contact with pets or humans and tests dead animals in areas previously free of rabies to see if the disease is spreading. It is, said Dettinger, "and very rapidly." The only area of the county that appears to be largely free of rabies is near Fort Belvoir and Mount Vernon, he said.

Most of Montgomery's new rabies cases also have been inside the Beltway. Five of the District's six cases, all dead raccoons found by passersby, have been along MacArthur Boulevard and are thought to have come from Montgomery. Of Montgomery's 119 cases since last October, all have been raccoons, except for three skunks, one bat and a beaver. The 54 county residents who had contact with the animals or with pets that had contact were given rabies shots, said county public health adviser Art Brown.

The only Prince George's rabies case was a raccoon trapped recently in Hyattsville by a resident.

Nine rabid raccoons have been found in Arlington since last July, two of them this year.

Prince William County, which had 55 rabies cases in 1982, has had seven cases this year--six raccoons and a calf--but it only investigates cases where there has been contact with humans or pets. Two residents have undergone rabies shots within the past few weeks.

Loudoun, which had 296 rabies cases in 1982, has had only 10 cases so far this year, the same as last, but like most area jurisdictions is conducting emergency vaccination clinics for cats and dogs to help protect residents against an expected increase in rabies this year.

Loudoun will hold a rabies clinic Feb. 12, Montgomery will give free vaccinations for cats Feb. 13 and for dogs Feb. 27, Prince George's will hold a clinic this Sunday, and other jurisdictions plan to schedule clinics during the winter and spring.