A Montgomery County judge delayed yesterday the enforcement of a new county measure that would have barred the county from doing business with the C&P Telephone Co. next week if C&P did not lower certain rates for customers in Gaithersburg and Montgomery Village.

Circuit Judge Rosalyn B. Bell, responding to a suit filed against the county yesterday by the C&P Telephone Co. of Maryland, issued an injunction that will postpone enforcement of the measure until the issue has been resolved in court. A trial is expected sometime next spring, according to county officials.

C&P argued in the suit that it could not legally apply the new rates--which would have lowered the charges for up-county residents who now pay more than down-county residents for calls to some parts of Northern Virginia and Prince George's County--without approval of the Maryland Public Service Commission.

Montgomery officials were concerned the county was threatened with losing all its telephone service--including police and fire calls--if the measure went into effect as scheduled next Thursday.

The measure, pushed by state Del. Robin Ficker of Potomac, who lost a bid for reelection in November, was approved at a referendum by 54 percent of the county's voters as an amendment to the county charter. County officials had considered taking action of their own to prevent the measure from going into effect. The C&P suit turns out to serve their purpose.

The judge's injunction can be challenged, but in order for it to be reversed there must be proof that the county will suffer irreparable damage if the measure does not go into effect on schedule.