HOBOKEN FOR MOST people who live on the clean, tree-lined streets of Hoboken's brownstone revival neighborhoods, life is comfortable. The homes are well kept and an air of a community is on the rise.

But for many residents of the city's less-fashionable tenements, fear, not comfort, is their constant companion. Standing outside the five-story tenement in which she lives, Brigita Rodriguez said: ''I have three children, and I'm afraid for them. Me and my husband, I don't care so much, but our children -they're afraid.'' And with good reason. On Oct. 24, the building next door, at 1202 12th Street, caught fire at 4 A.M. Within two hours, 11 of its 21 tenants, including seven children who once played with Mrs. Rodriguez's youngsters, were dead.

That blaze was the second fatal fire here in three weeks. The first, in the early hours of Columbus Day, killed two brothers 7 and 2 years old.