It is as if the producers of "The Fire Next Door" were of two minds.

Having first jolted viewers tonight with an apocalyptic vision of our big cities in flames - arson has become the nation's fastest growing crime - they pull back to assure us that the best in the human spirit can, indeed, reverse what they've suggested may be irreversible.

Each viewer will have to decide just how convincing each argument is in this CBS Reports, which airs at 8 on Channel 9, pre-empting "Who's Who." It is, finally, a test of one's opinion of mankind.

In the first 30 minutes or so, the case for the fiery end to our cities is powerfully made by correspondent Bill Moyers, the camera crews who take us into the crackling hell of the South Bronx and through the words of policemen who have lived too long with the urban nihilism of the unwanted and uncaring.

In the South Bronx, 30 fires are being set every day in that once-handsome borough of half a million.

Vandals vie with tenants to burn their pitiable territory in the name of greed or in thoughtless revenge against landlords, who themselves can buy for $200 an efficient "torch" job that will recover their federally granteed property insurance.

Just when tonight's picture seems most bleak (at, one point, a woman's apartment is ransacked as Moyers talks to her on the sidewalk), the program shifts emphasis.

Viewers meet a brave, good-immored woman named Mrs. Barclay who unwittingly sketches a self-portrait of the hopeful heart earning its combat pay while Moyers conducts a tour of current self-help projects that seem to offer promise.

Yet the viewer can't ignore his observation that U.S. officials, like the public, are more concerned with foreign problems that seem solvable than with domestic failures that seem to "paralyze our will."

Moyers himself seems dubious about the efficacy of his prescription for "capital, jobs and enough time" to save the South Bronxes that exist in most big American cities. It was a prescription that did not work in the 1960s, when he helped draw it up as a member of President Lyndon Johnson's staff.