The number of federal workers fired for poor performance -- currently about 1,200 a year -- is expected to increase dramatically in the very near future, the office of Personnel Management said yesterday.

But in the long run, it won't make that much difference, OPM acknowledges, because they expect the number of annual misconduct firings, currently about 11,000, to drop. This comes in the wake of a ruling last week by the Merit Systems Protection Board that appears to make it easier to fire poor performers.

OPM General Counsel Joseph Morris said yesterday that in the past, many managers and supervisors found it easier to justify dismissals of employes by charging them with misconduct, even when the real reason was poor performance because the latter were more easily overturned.

Non-federal employers are generally less likely to hire a worker fired for misconduct.

The Carter administration persuaded Congress to pass the Civil Service Reform Act largely on its claim that it was next to impossible to fire employes for poor performance.

The reform act also created the protection board, which was to act as a watchdog of employes' rights. It was given the authority to overturn agency disciplinary actions against employes it found to be illegal, improper or taken to punish employes for whistle-blowing activities.

The board also had the authority to lessen penalties against employes alleged to be poor performers.

But earlier this month the protection board decided it should not review poor performance penalties against employes imposed in accordance with agency rating systems and approved by OPM.

In a statement yesterday, OPM Director Donald J. Devine said new guidelines for firing are on their way to federal agencies. Managers and supervisors will be told that the administration will back them up if they document their cases correctly, he said.

OPM is about to ask agencies to resubmit for approval the systems they plan to use to take action against employes.

Morris said he anticipates that the overall number of employes disciplined or fired for poor performance or misconduct will remain about the same. But he said he expects that more employes "who are indeed poor performers" will be fired for that reason, rather than being charged with misconduct.