Democratic presidential candidate Hillary Clinton on Sunday will unveil a major spending plan involving infrastructure and jobs, aides say. (Charlie Neibergall/AP)

Hillary Clinton will unveil the largest plank of her economic agenda in the coming weeks, proposing hundreds of billions of dollars in spending, primarily on infrastructure projects, according to campaign aides.

At a campaign event in Boston on Sunday, Clinton will preview her infrastructure proposal, and over the course of several weeks she plans to outline the remainder of her jobs plan, which calls for investments in manufacturing, clean energy and research funding.

The proposals constitute the largest amount of spending that the campaign has outlined thus far — exceeding the $350 billion that Clinton has proposed for a college affordability plan — all aimed at creating what the campaign calls higher-paying, ­middle-class jobs.

“Investing in infrastructure makes tremendous sense, both because it creates jobs that pay above median wages and because it improves overall productivity, which leads to higher incomes across the broader economy,” said Jake Sullivan, senior policy adviser for the Clinton campaign.

Clinton has long signaled that she would propose policies that require significant government investment — a repudiation of positions held by Republican candidates who favor smaller government.

The announcement also comes at a time when the former secretary of state still faces Democratic primary challenges from Sen. Bernie Sanders from Vermont and former Maryland governor Martin O’Malley, both of whom have campaigned on agendas that they say are more progressive.

Some conservative economists have concerns that infrastructure spending is an inefficient means of job creation and economic stimulus, largely because of government wastefulness.

“There’s cost overruns and all sorts of mismanagement with federal infrastructure spending,” said Chris Edwards, director of tax policy studies at the conservative Cato Institute. “There’s an issue with the quality of spending we’re getting from federal government.”

Democrats broadly support significant increases in infrastructure spending funded by the government. Clinton is also signaling her intent to woo moderate general-election voters with proposals to pay for the spending in ways that have garnered bipartisan support in the past.

The Clinton campaign is hoping to offer a clear choice to voters between a philosophy of cutting government and one that supports spending on public resources, said Austan Goolsbee, a former Obama administration economist who supports Clinton.

“They’re trying to offer to the American voter, ‘Please choose option A over option B,’ which is the Republican, ‘Let’s just cut taxes; let’s use our money to shrink everything about the government,’ ” Goolsbee said.

At the Sunday event, Clinton will discuss the infrastructure proposal and will be joined by Boston Mayor Marty Walsh (D) to launch a “Hard Hats for Hillary” coalition group consisting of unionized supporters in construction, building and transportation industries, campaign aides said.

Clinton’s plan proposes the creation of an infrastructure bank to leverage hundreds of billions of dollars in foreign and domestic private investment for infrastructure projects, an idea that has been supported by the Obama administration, transportation experts and both conservative and liberal economists.

The portion of the infrastructure and research investment plans that require federal spending would be paid for by closing corporate tax loopholes, including the “inversion” tactic that allows large corporations — most recently pharmaceutical giant Pfizer — to avoid U.S. taxes by moving their headquarters overseas.

Sanders, meanwhile, has already called for more than $1 trillion in infrastructure spending, paid for by corporate tax increases and higher taxes for the wealthy.

“Infrastructure investment is kind of a win-win for the economy,” said Princeton University economist Alan Krueger, chairman of the Council of Economic Advisers under President Obama. Krueger was consulted by the Clinton campaign on the economic plan. “In the short term, it puts more construction workers and manufacturing workers back to work. And those jobs tend to be relatively well-paid. They are particularly ­middle-class jobs.”