Government information comes in a variety of formats, including books, journals, websites, committee hearings, and more. For this reason, there is no single style manual exclusively for citing government sources. Each style guide will have rules for particular source types. A government published book, in other words, will be cited like all other books. Some style guides do have citation examples for more specific government publications.
The Complete Guide to Citing Government Information Resources is helpful in identifying bibliographic information for various government sources. However, it must be used in conjunction with whatever style manual you are using for the rest of your citations.
Online Guides for Government Sources
Guide: Citing U.S. Government Publications : Guide from based largely on Garner and Smith's The Complete Guide to Citing Government Information Resources (1993). You will still need to consult your specific style manual to fine tune these examples, but it is helpful in understanding the various types of government documents. (Indiana University Bloomington)
How to Cite US Government Documents in MLA, APA : Provides sample citations, mostly for legal and congressional materials, in APA and MLA styles. When the specific case is not addressed by the pertinent style manual, they look to the BlueBook for Legal Citation. (Cornell University Libraries)
Docs Cite : A step by step guide that helps you create citations for government publications using MLA or APA style. Uses a fill-in-the-blank template. As always, it is important to check any citation created via a generator against your official style manual. (Arizona State University)
Chicago Style Quick Guide for Government Documents : Provides sample footnotes and bibliographic citations in Chicago style. The examples are based on the 15th edition of the Chicago Manual of Style, since the 16th edition doesn't have as detailed instructions for citing government publications. (Bowdoin College Library)