A federal grand jury indicted Baltimore's chief prosecutor today on charges of halting a major public corruption investigation in return for election support and contributions from a powerful political boss.

The indictment charges that State's Attorney William A. Swisher allowed the boss, the late James H. (Jack) Pollack, to control the prosecutor's office after Pollack brought Swisher from political obscurity to the post in 1974.

The indictment is the latest in a long series of federal corruption charges against Maryland politicans, including former Gov. Marvin mandel, former Vice President Spiro T. Agnew, two county executives and several state senators and delegates.

It charges that Swisher, through Pollack, extorted $23,000 from the targets of a corruption investigation and that job seekers who were hired in the prosecutor's office made payoffs to Pollack.

The 45-year-old Swisher in 1974 challenged State's Attorney Milton B. Allen, the first black elected to a major office in Baltimore, with a campaign that called the city streets "a jungle." Black leaders accused him of racism, as they did again this year when he called looters who ransacked stores during the February snowstorm "animals."

Swisher is charged with 18 counts of mail fraud, three of extortion and six of income tax violations involving his alleged failure to pay taxes on more than $18,000 in 1974, 1975 and 1976.

Neither Swisher nor his attorney was available for comment on the indictment.

Baltimore citizens, the indictment charges, were defrauded of their right to Swisher's "conscientious" and "unbiased" service after he allegedly joined Pollack in a "corrupt relationship" in which Pollack provided political support and Swisher agreed to "act favorably"to Pollack's requests while in the prosecutor's office.

In 1975 Swisher allegedly arranged "the abrupt termination" of his office's investigation of Harford County contractor Charles E. Collison and Ottavio F. Grande, a top city building official and close friend of the mayor.

Pollack allegedly had demanded $25,000 from the two and $15,000 was allegedly delivered to him in June 1975 by George J. Santoni, then a member of the House of Delegates.

Swisher, the indictment charges, "aided and abetted" Pollack in the extortion scheme, and, in late 1975., "false and incomplete" records and reports were created in his office to conceal the true reasons for the investigation's abrupt end.

Grande was later convicted on federal charges of extorting kickbacks from contractors and Collison pleaded guilty to federal tax evasion charges stemming from the same investigation.

Attorneys for both men refused comment yesterday on the indictment. Santoni currently is serving a federal prison sentence for his conviction in 1977 on federal extortion charges.

Pollack, a legendary Baltimore figure who for years held unrivaled influence in state and city politics, supplied "substantial cash" to Swisher's 1974 election campaign, according to the indictment. It charges that as part of their "corrupt scheme" it was agreed that Pollack's name would not be listed in campaign fundraising reports to the state.

Once in office, Swisher allegedly hired individuals sent to him by Pollack, and job seekers and their relatives allegedly made payoffs to Pollack, although the indictment does nof state any amount. CAPTION: Picture, WILLIAM A. SWISHER, "corrupt relationship" described