The U.S. Secret Service faces the daunting task of providing security on the presidential campaign trail and for at least six major national security events in the coming year, its director said Wednesday.

Director Mark Sullivan told House members that 2012 will be “a very demanding and challenging year” as the agency provides protection for President Obama, Vice President Biden, their families, former presidents, visiting foreign dignitaries, GOP candidates and the Republican Party’s eventual presidential nominee.

The Secret Service is also preparing to provide security at six major political events in fiscal year 2012 — November’s Asia-Pacific Economic Cooperation Summit in Hawaii, the annual State of the Union address, next spring’s NATO summit and G-20 meetings in Chicago, and next summer’s Republican convention in Tampa and Democratic convention in Charlotte.

In the past two years, Secret Service special agents have provided 100 percent incident-free protection to dignitaries during more than 6,100 trips across the United States and about 560 overseas trips, according to Sullivan. In 2010, the agency provided security for visits by 236 foreign officials and their spouses — mostly during a nuclear security summit in Washington and United Nations meetings in New York.

In anticipation of next year’s workload, the Secret Service is requesting $113.4 million to cover security costs for GOP candidates during the 2012 campaign — a $4 million increase from the 2008 campaign and about two-thirds more than was spent for security during the 2004 election. (Most costs for protecting Obama and Biden will be paid for out of a separate budget request, according to agency officials.)

The agency wants an additional $19 million to pay for security at the large events.

Testifying Wednesday to a House Homeland Security subcommittee, Sullivan noted that calculating campaign security costs involves several variables, including an unknown number of major candidates; how, where and when they will travel; and how quickly the Republican Party may settle on a nominee.

During the 2008 campaign cycle, extra burdens forced the Secret Service to borrow more than 2,000 immigration and Transportation Security Administration officers to screen people attending large campaign rallies, and to scale back counterfeiting and cyber-crime responsibilities to pay for candidate protection. Special agents began protecting then-Sen. Barack Obama (D-Ill.) in May 2007 — the earliest a presidential candidate had ever received protection during a campaign cycle.

With the 2012 presidential campaign season underway, Sullivan said, Secret Service agents began training in May to join protective details for the GOP presidential candidates. Agents assigned to the campaign trail serve on 21-day shifts through the end of the campaign, or until a candidate drops out.

Overall, the Secret Service is seeking a $1.69 billion budget next year to fund security, intelligence, counterfeiting and cyber-crime missions. House and Senate appropriators differ on how much to grant the agency overall, but budget plans drafted in each chamber would provide money for candidate protection.