The magnetic and transport properties of <$E roman {La sub 0,7 Ca sub 0,3 MnO sub {3- delta}}> films with an oxygen deficiency (<$E delta><$EB0> 0,1) and a <$E roman {La sub 0,9 Ca sub 0,1 MnO sub 3}> film with the stoichiometric oxygen content are investigated in a wide temperature range. It is shown that the charge-ordered insulating (COI) state is observed for a <$E roman {La sub 0,7 Ca sub 0,3 MnO sub 2,9}> film with thickness <$E d~symbol Г~30> nm, which manifests mainly a cubic crystal structure with an anomalously small lattice parameter for this composition. An increase in the fullm thickness (<$E d><$B0> 60 nm) leads to a structural transition from the lattice-strained cubic to the relaxed rhombohedral phase, is accompanied by a shift of the Curie point (<$E T sub C>) to lower temperature and a frustration of the COI state. The magnetic and transport properties of the <$E roman {La sub 0,7 Ca sub 0,3 MnO sub 2,9}> fim with <$E d><$B0> 60 nm are similar to those exhibited by the optimally oxygen-doped <$E roman {La sub 0,9 Ca sub 0,1 MnO sub 3}> film. It is concluded that the formation of the COI state in the <$E roman {La sub 0,7 Ca sub 0,3 MnO sub {3- delta}}> compound is governed by a compression of the crystal lattice rather than accumulation of oxygen vacancies, the low doping of the substituder divalent ions, or electronic phase separation.

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