Passport Specialists
The approximately 665 Passport Specialists employed by Passport Services work at the 18 Passport Offices located around the county in Miami, Charleston, Washington DC (three offices), Philadelphia, Boston, Portsmouth NH, New York, Connecticut, New Orleans, Houston, Chicago, Los Angeles, San Francisco, Seattle, Colorado, and Honolulu. They are responsible for adjudicating passport applications, which involves determining whether an applicant is a U.S. citizen or national, whether an applicant is who he/she claims to be, determining whether there exists any bar to an applicant receiving a passport (e.g., being more than $2500 in arrears on child support), and applying other rules and regulations. These federal workers adjudicated 12.1 million passport applications in Fiscal Year 2006. Now that Western Hemisphere Travel Initiative has begun to be implemented (on January 23, 2007 for air travel), that number is estimated to reach 18 million. For statistics on passport issuances over the years, click on this link: http://www.travel.state.gov/passport/services/stats/stats_890.html 
OPM General Classification Schedules September 1993 edition of the Position Classification Standard for Passport and Visa Examining Series, GS-0967:
Position Classification Standard - PDF Document
Passport Specialists are Civil Service employees. Adjudicating passport applications is recognized as an "inherently governmental function":
State Department Memorandum
The number of Passport Specialists has grown from 440 on April 8, 2002 to 665 on March 5, 2007.  Here is a graph showing the number of bargaining unit employees and Passport Specialists who work for Passport Services:

Source: Lists of bargaining unit employees provided to NFFE Local 1998 (the Union that is the exclusive representative of Passport Services' employees), as required by Article 10, Section 4 of the collective bargaining agreement.   

Date Total # BUE Total # Passport Specialists Total # Passport Specialist Trainees
October 2, 2000 610  ? ?
April 8, 2002 626 440 14
September 6, 2002 627 435 14
August 27, 2003 611  ?  ?
January 11, 2005 654 480 29
October 24, 2005 635 505 24
June 26, 2006 749 586  ?
March 5, 2007 775 665 15

Notes:
* BUE = "bargaining unit employees". 
* The number of trainees is included in the total # of BUE, but is not included in the number of Passport Specialists. 
* The April 8, 2002 list from HQ included 642 total BUE, but 16 of them were supervisory or other non-BUE positions, so were subtracted.
* The September 6, 2002 list from HQ included 642 total BUE, but 15 of them were non-BUE and were subtracted.

 

 

Based on information from the travel.state.gov website and projections on passport issuance for Fiscal Year 2007, here is a chart showing an increasing number of passports being issued:

 

Updated March 21, 2007