The Time Hoppers

They were disappearing, one at a time, in spite of the fact that in the crowded, hungry world of 2490 there was really nowhere worth going. Then they began to reappear, not in Moscow or Nairobi or LA--but in 1970, 1981, even the nostalgic days of the roaring 2100's. A way to the past had been found & people were flocking thru it for a better life--no matter what peril they might pose to the threatened present.
Earth in the late 25th Century is an unpleasant place for many. People are crowded into most available areas. Unemployment is rampant. A highly stratified society provides luxury & space for a few, while lower levels live crowded in tiny apartments. Into this situation comes a hope of escape–-escape into the past, before the world was crowded.
The story follows several characters. 1st is Joe Quellen, a midlevel Secretariat of Crime bureaucrat with a secret African residence, reached by a private teleportation booth. He heads the investigation into unauthorized time travel. Another is Norman Pomrath, Joe's brother-in-law, an unemployed low-level worker. He swears he wouldn't abandon his wife & children if presented with a chance to become a hopper.