  For a flux qubit described by a two-level system of equations we propose a
special time dependent external control field. We show that for a qubit placed
in this field there exists a critical value of tunnel frequency. When the
tunnel frequency is close to its critical value, the probability value of a
definite direction of the current circulating in a Josephson-junction circuit
may be kept above 1/2 during a desirable time interval. We also show that such
a behavior is not much affected by a sufficiently small dissipation.
