A General Accounting Office study released yesterday says firing workers is about the most expensive option the government has when it is trying to cut payroll costs.

Some politicians love to fire bureaucrats to win votes back home. But the congressional watchdog agency says it isn't a cost-effective way to run a business, or a government. It's better, GAO says, to slim down by not filling jobs when they become vacant, or by furloughing workers.

During the first three years of the Reagan administration, about 12,000 government employes in 42 agencies lost their jobs because of reductions-in-force. About 2,900 of the RIFs occurred here. Morale, and with it production, slumped in many agencies.

Because of the ripple effects of the RIFs, many thousands of civil servants were downgraded or transferred to other jobs. Senior employes whose positions were abolished sometimes bumped younger (and lower paid) workers out of their jobs.

GAO's study dealt with RIFs at the Consumer Product Safety Commission, Energy Department, Labor Department, Transportation Department and Office of Personnel Management.

GAO auditors confirmed earlier reports by the Federal Government Service Task Force (a sort of congressional civil service caucus), which said that RIFs are costly and deal most severely with women and minorities, who often have the least seniority.

The RIFs produced a number of sad tales, among them being those of the Office of Personnel Management psychologist who dropped to a clerical job and the physician at the Department of Health and Human Services who wound up, after his job was abolished, as the highest paid (and probably least competent) typist in the government.

The GAO said cost to the government of downgrading (placing higher-paid employes in lower-level jobs) ranged from $5,026 at the General Services Administration to more than $10,000 at the Occupational Safety and Health Administration and the Consumer Product Safety Commission. In addition, GAO said that when the RIFs permit employes to retire earlier than usual, additional lifetime costs are imposed on the civil service retirement system because the workers contribute money for a shorter time and draw benefits longer.

While noting that layoffs are the "least humane" way to trim staff, the GAO study concentrated on the dollars-and-cents costs versus savings to the taxpayers of RIFs. And it concludes that because the government is required to pay some employes severance (up to one year's salary), plus lump-sum benefits and unemployment benefits, the government can save a lot less by firing an employe than by trimming in other ways.