THE ISSUE is a pay raise. District government workers say they should get the same pay raise this year that federal workers are getting. Mayor Barry's response has been, briefly, "No." The mayor says that all the city can afford, as it goes through its current financial crisis, is a 5.1 percent increase. And he notes that the 5 percent is all that has been appropriated for a pay raise in this year's already completed city budget.

That straightforward response has been clouded, however, by the unions' complaint that the ciy government has violated the new labor relations law. Under that law, the amount of any pay raise for city employees must be negotiated. Mayor Barry points out that the unions had an entire year to request negotiations over the amount of their pay increase in the 1981 fiscal year. They did not make that request until just days before the fiscal year began on Oct. 1. In addition, the city's chief negotiator, Donald Weinberg, says the legal mechanics for negotiating a pay raise have not yet been constructed. The unions should forget negotiating a pay raise for this year, in his view, and wait until next year.

For city workers who are battling inflation like everyone else, Mr. Weinberg's words are cold comfort. That he should suggest they forgo a pay raise because of a bureaucratic problem is not a reasonable request. But neither is it reasonable for the unions to enter a last-minute request for negotiations and base their demands on the premise that they are entitled to pay equal to that of federal government employees. The city government is no longer tied to the federal civil service system and has no obligation, not even a tacit one because of past links to it, to pay city workers what federal workers receive.

The unions should have been pushing for a larger raise long ago if that is what their members want. And the unions as well as the workers must realize that these are not the best of times for the city's treasury. Any request for a pay raise must be viewed in terms of that severe financial strain. From that perspective, a 5 percent pay raise does not look as bad as it does when compared with the raise federal workers are getting.