A federal appeals court yesterday barred the federal government from instituting controversial shifts in regulations governing pay raises, layoffs and other personnel practices for government employes.

In an order signed by two judges, the U.S. Court of Appeals here temporarily blocked the Office of Personal Management from imposing the revised rules, which had been scheduled to take effect tommorrow.

The appeals court said its order was designed to allow time for a U.S. District Court judge to rule on the issue.

The order, signed by Judges Patricia M. Wald and Harry T. Edwards, warned of "immense, far-reaching and possibly irreparable consequences for virtually all employes throughout the federal government" if the revamped rules were instituted without court review. It directed the lower court to reach a decision by July 10.

The revised regulations were drawn up by the Reagan administration in an attempt to put more emphasis on federal workers' performance and less on seniority. The rules are expected to make it more difficult for employes to gain regular pay increases and to weaken job security for longtime employes.

The shift would affect longevity pay raises, reductions in force and other procedures for 1.2 million white-collar government workers.

Congress twice has barred the Office of Personnel Management from imposing the revised rules. The latest congressional prohibition will expire tomorrow. After its July 4 recess, Congress is expected to consider a renewed ban against the proposed rules.

The appeals court's decision was hailed by a lawyer for the American Federation of Government Employees, which had challenged the revised regulations in court. William J. Stone, assistant general counsel for the 700,000-member union, described the court opinion as "very strongly worded" and said, "It strongly supports AFGE's opinion."

On Friday, U.S. District Court Judge Thomas Penfield Jackson had turned down an initial request by the union to block the revised regulations. The union then sought a similar order from the appeals court. The 110,000-member National Treasury Employees Union joined in the lower court challenge, but did not take part in the appeal.

It was unclear yesterday whether the Justice Department would seek to appeal the ruling to the Supreme Court. Acting Assistant Attorney General Richard K. Willard could not be reached for comment.

The appeals court said its order was "not to be interpreted as an expression of a view with respect to the ultimate merits of the case." The court said it acted because of the significance and complexity of the issues.

In its five-page ruling, the court said the union had raised "several substantial legal questions." It cited the union's contention that the rules should be barred because of earlier court actions and because of alleged violations of administrative procedures.