Budget hawk John McCain took a fresh shot at Barack Obama Thursday, calling on him to publicly identify the “pork barrel” projects he sponsored in the Senate.

It was the Arizona senator’s latest attempt to simulate a general election and cut down Obama as he creeps ahead of Hillary Clinton in the tight race for the Democratic nomination. McCain was poised to move a big step closer to sealing the GOP nomination with the endorsement of former rival Mitt Romney Thursday.

McCain’s challenge to Obama was based on a Washington Post article that morning highlighting pork barrel project recipients. The article said Clinton helped lock down more than $340 million in earmarks for her home state of New York in last year’s spending bills, placing her in the top tier of Senate recipients for the type of localized federal spending against which McCain claims to be a crusader. By comparison, the article said Obama recorded $91 million in earmarks.

But McCain merely noted Clinton’s “pork” at a campaign stop in Burlington, Vt., and then blasted Obama for not revealing the target of his earmarks. The Post article said Obama has not released his letters to the Appropriations Committee seeking the earmarks for 2005 and 2006.

“The senator from Illinois, because he is a junior, had only gotten about $92 million, according to that article,” McCain said. “And the senator from Illinois, who says that he wants transparency in government, will not reveal the number of earmarks that he received in 2006 and 2005. Is that transparency in government? I don’t think so. I don’t think so!

“So I call on the senator … to go ahead and tell people how much money in earmarked projects and pork barrel projects that he got for his state and what they were for. And my friends, examine my record on pork barrel projects and you will see a big fat zero.”

The Post article cited a report from Taxpayers for Common Sense, which said McCain was, in fact, one of just five senators who rejected all earmarks.

But McCain’s comments escalate the brewing battle between him and Obama, as Obama takes the lead in the delegate count over Clinton.

Recent polls show Obama could be a stiffer challenge to McCain than Clinton. Head-to-head polls from the Associated Press, Time, CNN and USA Today taken in early February show McCain and Clinton in a dead heat in hypothetical match-ups. But they show Obama consistently edging out McCain by about 5 points or more.

McCain already has assumed the role of presumptive nominee given his wide lead over Mike Huckabee. Romney’s endorsement would only broaden that lead if he sends his delegates McCain’s way, as expected.

The Democratic race is far less settled, but Obama’s three-contest sweep in the Potomac Primaries gave him about a 55-delegate lead over Clinton, according to the latest Associated Press tallies.

Though McCain has gone after both Democrats for wanting to scale back forces in Iraq, McCain trained his sights on Obama Wednesday for being ranked the most liberal senator by National Journal, and attacked him for offering empty rhetoric, saying he’s “lacking in specifics.”

Former Sen. Rick Santorum said McCain is stepping up his attacks on Obama to stay in the limelight by going after the “media darling.”

“He needs to stay relevant. This race for the Republican nomination is all but over,” Santorum said.

McCain said Thursday he’s by no means counting out Clinton, who’s banking on big recoveries in the Ohio and Texas primaries March 4.

“I (don’t) underestimate the challenge of Senator Clinton,” he said, citing her against-the-odds victory in the Jan. 8 New Hampshire primary. “So I think it would be really a mistake to sort of discount the vitality of her candidacy. I am not an expert on this. I know she’s very, very smart, a very, very tough campaigner, and I think she’s proven.”

Obama’s trading fire, and in Wisconsin on Wednesday criticized McCain for switching positions to support the Bush tax cuts.

“Somewhere along the line, (McCain) traded those principles for his party’s nomination, and now he’s for those tax cuts,” he said.

Click here to read the story about Obama’s and Clinton’s earmarks in The Washington Post.

FOX News’ Mosheh Oinounou contributed to this report.