The Montgomery County library system, forced to reduce staff, cut back operations and shorten hours this year because of county budget constraints, will get an infusion of funds designed to halt its continued deterioration.

Under a program unveiled yesterday by Montgomery County Executive Charles W. Gilchrist, the county will try to maintain the level of existing services and replenish the system's book collection over a three-year period while adding a security system, stabilizing staffing and service hours and preparing for technological improvements.

Gilchrist said he will add $500,000 to the new $1.1 million library budget request for books, recordings and other items and authorize reallocation of already-available funds for an additional $242,0000 for books for the heavily-used Gaithersburg library. He also said he will seek $208,000 for a system designed to prevent book thefts. Thefts cost the library system about $107,000 a year.

Although the library department's budget share for the current fiscal year rose by 12 percent to $10 million, the cost of running two new libraries, salary increases and inflation took up most of the increase.

Earlier this year, many of the county's 19 libraries began staying closed two mornings a week to save money, and waiting lists for popular new novels were outstripping availability. Only 45 percent of the people who enter a county library find what they are looking for, compared with a figure recommended by the state of 70 percent.

Gilchrist said that the plans will not reverse past policies, but will represent an effort to maintain as high a level of services as possible. The executive has no plans to increase library hours, for example, but to maintain current hours and service.