The British colonial administration announced yesterday that it has authorized the Rhodesian Army to maintain law and order, Washington Post correspondent Jay Ross reported.

The move could lead to renewed fighting between the Army and the Patriotic Front guerrillas despite the cease-fire.

A British spokesman linked the action to the failure of a "substantial" number of guerrillas to report to assembly camps as required under the cease-fire agreement reached last month in London.

The agreement stipulates that the Rhodesian Army was to disengage to the vicinity of its bases and the guerrillas were to report to assembly camps by Friday midnight.

Maj. Gen. John Acland, British chairman of the cease-fire commission, said that 18,500 guerrillas had reported to the camps, but he said it was too early to assess the significance of the number.

Nicholas Fenn, spokesman for the British governor, Lord Soames, said a number of mujibahs , unarmed youths used as runners by the Patriotic Front, had reported to the camps after being armed and put in uniform to pass as guerrillas, thus inflating the count and allowing true guerrillas to remain at large.

Fenn said that because of the unknown number of guerrillas still at large and continuing incidents of lawlessness in the country, Soames had authorized the Army to help the "thinly stretched" police maintain law and order.

"It is not, however, the intention," he said, "that the Patriotic Front forces should be indiscriminately attacked."

Acland said he would not be able to give an authoritative assessment of the number of guerrillas who reported until midweek. The Rhodesian Army has estimated the number of guerrillas in the country at 15,000, while the Patriotic Front said the figure exceeded 31,000.

Spokesman Fenn admitted that South African units are in Rhodesia. With the agreement of the governor, he said, they are guarding the Beit Bridge border crossing in the south to protect the rail and road routes. He declined to give a figure but said the number was "not large."