WASHINGTON — Although he's the presumptive Republican nominee for president, John McCain has yet to ask for Secret Service protection as he travels the country.

The revelation surprised some members of Congress on Thursday during a hearing on the Secret Service's budget request for fiscal year 2009.

McCain's campaign has spoken about security with Department of Homeland Security officials, but the candidate has yet to ask for coverage, Secret Service Director Mark Sullivan said.

"He's not required to have protection," Sullivan said.

McCain campaign spokesman Jeffrey C. Sadosky refused to discuss security measures or Secret Service protection.

McCain said last fall that he'd avoid Secret Service protection as long as possible because it would interfere with his ability to interact with voters.

The absence of protection for the Arizona senator means that a lot of the agency's $110 million budget for presidential protection this fiscal year has gone primarily to the two high-profile Democratic nominees, Sens. Barack Obama of Illinois and Hillary Clinton of New York.

Clinton already was entitled to some protection as a former first lady, but Secret Service staffing levels were adjusted after she became a presidential candidate.

Obama began using Secret Service protection after Homeland Security Secretary Michael Chertoff and a bipartisan advisory committee decided last May that threat levels were high enough to warrant it.

The high staffing levels have strained the Secret Service, which didn't begin protecting Democratic nominee John Kerry until February 2004 in the last presidential election cycle. Sullivan said that the agency had faced "challenges" with massive crowds, not usually seen in the winter and spring before an election.

The agency has protected candidates at more than 1,000 events so far in this election cycle. It's put more than 550,000 visitors through magnetometers to screen for guns or other weapons. And it's spent more than 700 days protecting the two top Democratic contenders.

For voters, the difference between attending campaign events with and without Secret Service agents can be huge.

When former North Carolina Sen. John Edwards was still on the trail, for example, he freely visited voters in town hall meetings and coffee shops with no obvious security.

At Obama and Clinton events, Secret Service agents sweep locations with specially trained dogs, often forcing bystanders to wait in lines outside. Somber security agents in suits and earpieces patrol audiences during speeches and shield the candidate during handshaking sessions with well-wishers.