Executive director Adam Parkhomenko and communications director Seth Bringman work at the offices of Ready for Hillary, a new super PAC that aims to encourage Clinton to run for president, in Alexandria, Va., on Thursday. (Mary F. Calvert/FOR THE WASHINGTON POST)

The campaign has a flashy Web site and official logo T-shirts and signs. Prominent Democrats have endorsed it and written $25,000 checks. Its paid operatives and volunteers have set up shop in an Alexandria strip mall office that last housed the regional campaign headquarters for Sen. Timothy M. Kaine (D-Va.).

All it needs now is a candidate.

The upstart super PAC, called Ready for Hillary, is fast emerging as the quasi-official stand-in for potential 2016 presidential contender Hillary Rodham Clinton, scooping up advisers and gathering big donations more than three years ahead of election time.

But the group is also making some advisers in Clinton’s orbit decidedly nervous about its potential impact on her own efforts, which for now consist of philanthropic pursuits and remaining mum on a presidential bid. Some allies also fear a repeat of 2008, when an assumed air of inevitability contributed to Clinton’s loss to fresh-faced challenger Barack Obama.

Super PACs and other independent groups, which rose to prominence in the 2012 campaign, can cause serious problems for candidates they aim to support by going off message or muddying the landscape. Some donors are already confused by a proliferation of pro-Clinton groups, including at least three registered super PACs that feature Clinton in their name.

“It’s hard to even know what’s what any more,” said John Morgan, an Orlando lawyer who served on Bill Clinton’s 1996 national finance committee. “It’s become a cottage industry. It’s like, ‘Who are you?’ Just because you put the name ‘Hillary’ at the end of your PAC — it could be a bait and switch. I want to make sure I can get the biggest bang for my buck.”

Ready for Hillary — launched in January by Clinton boosters Adam Parkhomenko and Allida Black — is getting help from a number of veterans from Hillary and Bill Clinton’s political operation. Former Bill Clinton strategist Harold Ickes, former Clinton White House political director Craig Smith and former Hillary Clinton campaign lawyer Jim Lamb are advising the group on strategy, while longtime confidant James Carville recently sent out a fundraising solicitation under his name.

“I look at this as an outpost that will help Hillary if she runs,” Ickes said.

“There are likely to be a number of Hillary super PACs popping up like mushrooms in the spring,” he added, but “this super PAC is the real deal.”

Super PACs are not allowed to coordinate their message or spending with any candidate or political party, and Ready for Hillary organizers say they have had no contact with Clinton or those in her immediate circle of advisers. The Clinton camp says the same.

“They are an independent entity acting on their own passion,” said Nick Merrill, a Clinton spokesman. “Their energy and enthusiasm to convince her to run is inspiring, though only she in the end can make that very personal decision.”

Still, enough boldface names close to the Clintons are involved to give Ready for Hillary “the official ‘Good Housekeeping’ seal of approval for all things Hillary,” said Michael Trujillo, an adviser to a rival super PAC.

Leading the group’s fundraising efforts are former California congresswoman Ellen O. Tauscher and Shelly Porges — both of whom worked for Clinton at the State Department — as well as Esprit co-founder Susie Tompkins Buell and Miami developer Christopher G. Korge, who served on her 2008 campaign finance committee.

A host of former Clinton insiders have also given money to the group, according to organizers and donors, including former Clinton political adviser Ann F. Lewis.

Several Clinton associates said they have received no indication from Clinton about whether she approves of the group.

“There are no winks; there are no nods,” Buell said.“We’ve all gotten a yellow light — we haven’t heard, ‘This is great, do it,’ and we haven’t heard, ‘This is not good, don’t do it.’ ”

After Clinton lost in 2008, her key advisers tried to keep an informal network of supporters going through a nonprofit group called No Limits Foundation, but Lewis said it folded in 2012. Lewis said Clinton plans to stay out of politics at least until she publishes a book next summer.

Ready for Hillary has been reaching out to prominent 2008 Obama supporters, hoping to prove that Clinton’s political base has expanded to incorporate Obama’s. Atop its list was Sen. Claire McCaskill (D-Mo.), who as an Obama surrogate publicly attacked Clinton. This week, she formally endorsed the super PAC — prompting a call of thanks from Clinton, McCaskill said.

Parkhomenko, 27, the group’s executive director, said the super PAC plans to open chapters on college campuses this fall and to recruit volunteer leaders in top battleground states to recruit their neighbors and friends.

“We can activate them should she decide to run,” he said.

The main advantage super PACs have over campaigns is the ability to raise unlimited amounts of money. Ready for Hillary, with a paid staff of five, will file its first donor disclosure reports in July. It says it has finance consultants working in five states and the District.

But, in an unusual decision, the group says it is capping donations at $25,000 per person, which organizers believe gives it a grass-roots sheen. Parkhomenko said donors have asked to contribute more than $1 million but that he has turned them down.

Former Michigan governor Jennifer Granholm (D), a Ready for Hillary donor, said the super PAC will also give Clinton an organizational edge if she decides to run. Election lawyers said the group could probably share voter data with an eventual campaign through a list exchange.

“Her lists are old, and her supporter contacts may be a little dusty,” Granholm said.

Unlike Priorities USA — which was run by former White House aides and whose strategy largely aligned with the president’s reelection campaign — Ready for Hillary is being run by relatively less experienced operatives who are more removed from Clinton’s inner circle.

One person in Democratic politics close to Clinton who did not want to be identified as critical of the outside efforts said the super PAC might “create a lot of chaos.” Others fret that Ready for Hillary could push Clinton into partisan politics earlier than she would like.

“I worry that this effort — while very well-intentioned — kind of shortens the life span of the icon and lengthens the life span of the politician. You kind of grimace,” said one Clinton campaign veteran, who spoke on the condition of anonymity to speak candidly.

Meanwhile, some top GOP operatives have begun a “Stop Hillary” movement through the new super PAC America Rising. The group aims to “define the real Hillary,” according to a fundraising solicitation sent Thursday by co-founder Matt Rhoades, who managed Mitt Romney’s 2012 presidential campaign.

“The Clinton Machine is extremely powerful, and we have seen it in action time and time again,” Rhoades wrote. “We need to stop it before it is too late.”

For now, at least, the machine is gearing up in a drab office near a nail salon and Chinese takeout restaurant outside the Beltway in Alexandria. The windows are painted over, and the carpet is stained. A handful of volunteers sat around Ikea tables one afternoon this week stuffing envelopes with more than 30,000 Ready for Hillary bumper stickers — one for everyone who has signed up on the Web site.

Soon, Parkhomenko says, the group will sell goods online. One planned item that he’s particularly enthusiastic about is a line of T-shirts — “Bill for First Gentleman,” “Bill for First Lady,” and “Bill for First Lad.”

Karen Tumulty contributed to this report.