The job of protecting presidents started in 1894 with Grover Cleveland, who was guarded part time. That role expanded after the assassination of William McKinley in 1901, and it became a crime to threaten the president in 1917. Today, guarding the president and other top officials accounts for most of the Secret Service’s budget, which totals about $1.4 billion per year and continues to grow.

Its mission soon expanded to investigating the Ku Klux Klan and conducting counterespionage operations during the Spanish-American War and World War I.

The Secret Service, long under the Treasury Department but now part of the Department of Homeland Security, was established in 1865 to thwart counterfeiting, a focus that has expanded to include a host of electronic and financial crimes.

The financial crimes mission remains robust as well, he added, citing some recent large seizures of counterfeit currency.

Asked about the concerns, Special Agent Edwin Donovan, a Secret Service spokesman, said that though “there is no doubt the protection mission has grown,’’ the agency can still fulfill both its missions.

“The network and mainframe system used today struggles to support basic operations,’’ the agency said, requesting an additional $33 million over last year for computers and other information technology.

Already, there are signs of strain on the agency, officials said. Budget documents submitted to Congress this year said the agency lacks the necessary technology to keep up with threats.

“This is a discussion going on not only in some quarters in Congress, but inside the Secret Service. Should there be a re-look at the mission?’’ said a government official, who like others was not authorized to speak publicly about security matters or reveal details about the number or nature of the threats.

The report, which was provided to the Globe, said such a review should look at how money and staff are allocated, and whether some of the agency’s functions and workers should be transferred to the Treasury Department.

“If there were an evaluation of the service’s two missions, it might be determined that it is ineffective . . . to conduct its protection mission and investigate financial crimes,’’ according to a inter nal report issued in August by the Congressional Research Service.

The new demands are leading some officials, both inside and outside the agency, to raise the possibility of the service curtailing or dropping its role in fighting financial crime to focus more on protecting leaders and their families from assassination attempts and thwarting terrorist plots aimed at high-profile events.

The Secret Service is tracking a far broader range of possible threats to the nation’s leaders, the officials said, even as it also investigates financial crimes such as counterfeiting as part of its original mandate.

WASHINGTON - The unprecedented number of death threats against President Obama, a rise in racist hate groups, and a new wave of antigovernment fervor threaten to overwhelm the US Secret Service, according to government officials and reports, raising new questions about the 144-year-old agency’s overall mission.

The agency has been directed by Congress to guard what it describes an “unprecedented’’ number of individuals, including presidents, vice presidents, their immediate families, former presidents and vice presidents, and visiting dignitaries - as well as presidential candidates during campaigns lasting longer than ever before.

The Service currently protects 32 people - 24 full time and eight part time. It also coordinates security at high-profile events, such as meetings of world leaders and political party conventions. Between Oct. 1, 2008, and Sept. 30, the Secret Service said it protected 116 heads of state and 58 spouses.

“The service’s protection mission has increased and become more urgent, due to the increase in terrorist threats and expanded arsenal of weapons that terrorists could use in an assassination attempt or attacks on facilities,’’ according to the congressional report.

The domestic threat is also growing, fueled in part by Obama’s election as the nation’s first black president, according to specialists who study homegrown radical movements.

Obama, who was given Secret Service protection 18 months before the election - the earliest ever for a presidential candidate - has been the target of more threats since his inauguration than his predecessors.

Two days before Obama’s appearance at San Francisco fund-raisers on Thursday, a 59-year-old Northern California man was indicted on charges of sending a racist, profanity-filled e-mail threatening to kill Obama and his family. The rambling e-mail included specific references to Michelle Obama and the phrase, “do it to his children and family first in front of him,’’ according to the indictment.

The Southern Poverty Law Center says that antigovernment militias and white supremacist groups have strengthened in recent years, responding to an increasingly diverse population and what they see as an expanding government.

A center study released in August found a nearly 35 percent growth in racially based domestic hate groups since 2000 - from 602 to 926. The center concluded that opposition to Obama’s election has only increased the phenomenon.

“A key difference this time is that the federal government - the entity that almost the entire radical right views as its primary enemy - is headed by a black man,’’ the report said. “One result has been a remarkable rash of domestic terror incidents since the presidential campaign, most of them related to anger over the election of Barack Obama.’’

Threatening language has also found its way into talk radio broadcasts and social networking websites, raising fears that individuals not normally considered threats to the president could be incited to violence.

For example, the Secret Service in recent months has investigated a poll posted on Facebook about whether Obama should be killed. It has interviewed a Florida radio talk show host after a caller mentioned ammunition, target practice, and the president, and federal officials have raised concerns about several instances in which protesters carrying weapons showed up at Obama events, including a man at an August town hall in New Hampshire.

“The racist extremist fringe is exploiting themes that strike a chord in the mainstream more than we have seen in the recent past,’’ said Brian Levin, director of the Center for the Study of Hate and Extremism at California State University-San Bernardino, citing several elected leaders who have questioned whether Obama is a US citizen eligible to be president.

The Secret Service has been given more resources to deal with the changing environment. Its total number of employees has risen from 6,700 two years ago to a projected 7,055 in the new fiscal year that began Oct. 1, with almost all the new positions for the protection mission.

Its overall budget request has grown by several hundred million dollars a year, including a nearly a 20 percent increase since 2008 for so-called protective intelligence activities, the efforts to analyze and investigate threats, according to budget documents.

But a significant share of the agency’s budget still goes to investigating financial and other crimes, including 142 field offices nationwide and 22 overseas that also assist the search for missing and exploited children. A new proposal in Congress would allocate $20 million next year for the Secret Service to expand its role and investigate mortgage fraud.

“The establishment of a single mission, or a distinct primary and secondary mission, for the [Secret Service] is one option for Congress,’’ the congressional report said. “One argument for this is that the majority of the Service’s resources are used for its protection mission, and that Congress has raised the issue of the Service’s competing missions of protection and investigation.’’

Bryan Bender can be reached at bender@globe.com.

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