The 50th anniversary of the National Labor Relations Act comes at a time not of celebration but dispute. In a series of decisions mostly freeing employers from past restraints, Reagan administration majorities on the National Labor Relations Board have affected the balance of power in the work place. Even before these decisions labor wanted to amend the act; it tried in 1978 but failed. Now some labor leaders have said -- and only in part for the shock value -- that they might be better off if the act were repealed. The NLRA is the nation's fundamental labor law; it was written to bring labor disputes off the street. But the largest union in the AFL-CIO, the United Food and Commercial Workers, has now announced it will conduct its organizing drives where possible outside the NLRA framework, which it says is more hindrance than help.

The unions say that the Reagan board has unbalanced the law, taken it to extremes. They offer a long list of examples, some minor, some major. Thus the board has relaxed old rules meant to keep employers from making either threats or special promises to employees during organizing drives. It has weakened rules meant to safeguard the right of pro-union employees to sign up union members on company premises during the work day. It has indicated it will no longer protect against retaliation workers who turn their employers in to public agencies for violating health and safety laws. On a broader issue, it has expanded the right of employers to transfer work from union to non-union plants.

The board and its defenders say that this labor rendering of the record is itself unbalanced, that the Reagan board is simply redressing the tilt of its Carter predecessor and that the current swing is no different from others when the board has changed party hands in the past. They note that on several issues the courts have upheld the Reagan board; the Supreme Court last week upheld a board ruling that unions may not bar members from resigning during or just before a strike.

But many of the precedents the new board has altered date not from the Carter administration but the Nixon-Ford years and before. In routine cases involving charges of unfair labor practices, moreover, the Reagan board has held for management much more than either the Carter or Nixon-Ford boards, whose records were about the same.

We think the Reagan board has gone too far. The issue is not so much labor versus management as it is economic health. The Reagan board's holdings point to continuing low-level labor-management strife that an already burdened economy should not have to bear. Labor unions themselves have done some damage to the economy, taking some U.S. industries out of competitive range; in recent years they have paid for this, in lost work and at the bargaining table. But unions on balance are constructive institutions now in weakened condition, and public policy should not seek to diminish them.