APA rules for citing government publications follow the same basic format as other forms of publication.  Provide all of the basic elements that are available within the source.  If a citation element is missing from your document, just move on to the next required element.

Basic format:

Author/Corporate author.  (date).  
   Title of work. Retrieved from 
   http.//www.webpage.gov 

 The Corporate author is the government agency which wrote or sponsored the publication.  The corporate author / agency name needs to include the full hierarchy for the agency: start with the overseeing department name and then list the smaller "subdivision" agencies.  

Do not use acronyms or abbreviations, except for "U.S."

Example: 

 U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute.

Most will have a corporate author rather than a personal author.

Corporate author. (Year, Month/Date/Season). Title of article. Title of Journal, Volume(Issue), Page(s). Retrieved from http://www.departmentname.gov

Centers for Disease Control and Prevention. (2010, April 2). Interim results: State-specific influenza A (H1N1) 2009 monovalent vaccination coverage - United States, October 2009-January 2010. Morbidity and Mortality Weekly Reports. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5912a2.htm

A "data set" includes raw data (which might be imported into a spreadsheet for further manipulation) or interactive data displays.  (For complete details, see the APA Manual, 7.08.54.)  If there is no personal author, use the government agency as a corporate author. 

Author.  (Year).  Title of data set [Data file].  Retrieved from http://webaddress.gov

Centers for Disease Control, Behavioral Risk Factor Surveillance System.  (2008). SMART-BRFSS City and County Data (2008-Lincoln, NE Metropolitan Statistical Area) [Data file].  Retrieved from http://apps.nccd.cdc.gov/BRFSS-SMART/SelQuestion.asp?MMSA=48&yr2=2008&VarRepost=&cat

"Government Reports" include technical and research reports, census statistics (in PDF format or in print), reports of task forces, etc.  Format these reports as you would a book.  If there is no personal author, consider using the government agency as a corporate author. 

Author, A. A. (date).  Title of work (Report No. xxx).  Retrieved from 
      http://webaddress.gov

U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute.  (2003).  Managing asthma: A guide for schools (NIH Publication No. 02-2650).  Retrieved from http://www.nhlbi.nih.gov/health/
prof/lung/asthma/asth_sch.pdf

Nebraska Health and Human Services System. (2004). Nebraska adolescents: The results of 2003 youth risk behavior survey of Nebraska public high school students (grades 9 - 12). Retrieved from http://www.nlc.state.ne.us/epubs/H8250/B006-2003.pdf