Federal tax charges against Baltimore's chief prosecutor, William A. Swisher, were dismissed today in U.S. District Court after the government decided it would be unfair to pursue the case.

Swisher, 46, who was acquitted of political corruption charges six weeks ago, told reporters immediately following the brief hearing, "It is a delightful ending to a very long and bad experience."

The six tax fraud charges were dismissed after assistant U.S. attorney Daniel F. Goldstein told U.S. District Court Judge Alexander Harvey that "significant proof" in establishing Swisher's intent to evade more than $7,000 in taxes from an unreported $18,165 of income from 1974 through 1976 would have been evidence from the first trial.

Since Swisher was acquitted after that trial, the prosecutor said, "it would be unfair . . . to require him to defend himself again."

A federal jury cleared Swisher of 21 mail fraud and extortion charges last month. Swisher was acquitted of "selling his office" and stopping a sensitive investigation in exchange for political support from the late James H. Pollack. Part of the first trial included allegations that Swisher failed to report $3,920 of a bribe from two targets of the investigation who testified that they made the payoff in exchange for Swisher's cooperation.

Yesterday, members of the jury who had deliberated for 24 hours after hearing two months of testimony, said the government's case against the state's attorney was not strong enough.