A search for charginos and neutralinos, predicted by supersymmetric theorie
s, is performed using a data sample of 182.1 pb(-1) taken at a centre-of-ma
ss energy of 189 GeV with the OPAL detector at LEP. No evidence for chargin
o or neutralino production is found. Upper limits on chargino and neutralin
o pair production (<(chi)over tilde>(+)(1)<(chi)over tilde>(-)(1), <(chi)ov
er tilde>(0)(1)<(chi)over tilde>(0)(2)) cross-sections are obtained as a fu
nction of the chargino mass (m(chi 1)(+/-)), the lightest neutralino mass (
m(chi 1)(0)) and the second lightest neutralino mass (m(chi 2)(0)). Within
the Constrained Minimal Supersymmetric Standard Model framework, and for m(
chi 1)(+/-) - m(chi 1)(0) greater than or equal to 5 GeV, the 95% confidenc
e level lower limits on m(chi 1)(-/+) are 93.6 GeV for tan beta = 1.5 and 9
4.1 GeV for tan beta = 35. These limits are obtained assuming a universal s
calar mass m(0) greater than or equal to 500 GeV. The corresponding limits
for all m(0) are 78.0 and 71.7 GeV. The 95% confidence level lower limits o
n the lightest neutralino mass, valid for any value of tan beta are 32.8 Ge
V for m(0) greater than or equal to 500 GeV and 31.6 GeV for all m(0).