Cigarette smoking would be prohibited on U.S. airline flights of two hours or less for the next two years under legislation agreed to by House and Senate negotiators. The ban would affect 80% of all domestic routes and would take effect four months after final passage of the spending package. The agreement was reached by senators and representatives working on the transportation section of the $600-billion spending bill that would cover federal operations for the 1988 fiscal year. Under the language accepted by the negotiators, passengers caught smoking would be subject to fines of up to $1,000. In addition, a $2,000 fine would be imposed on passengers caught tampering with smoke detectors in airliner restrooms.