  Transverse momentum event-by-event fluctuations are studied within the
string-hadronic model of high energy nuclear collisions, LUCIAE. Data on
non-statistical pT fluctuations in p+p interactions are reproduced.
Fluctuations of similar magnitude are predicted for nucleus-nucleus collisions,
in contradiction to the preliminary NA49 results. The introduction of a string
clustering mechanism (Firecracker Model) leads to a further, significant
increase of pT fluctuations for nucleus-nucleus collisions. Secondary hadronic
interactions, as implemented in LUCIAE, cause only a small reduction of pT
fluctuations.
