President Obama’s plan to fund his $447 billion jobs-stimulus bill by limiting tax breaks for wealthier people is getting a wary reception from arts organizations, which fear that the proposal could cut into already diminishing donations to museums, symphonies, ballets and other groups.

The president’s proposal would raise a projected $400 billion over 10 years by reducing the amount families with gross incomes of more than $250,000 a year (and individuals earning $200,000 and up) can deduct on their tax returns. It would limit those individuals to writing off 28 percent of their itemized deductions, down from 35 percent. Such deductions include mortgage interest and charitable donations.

It’s this last part that makes nonprofit groups in general, and arts organizations in particular, nervous.

Obama’s plan means that wealthier donors would save $2,800 in taxes on a $10,000 charitable contribution, instead of the $3,500 allowed under current law. The proposed change would go into effect in 2013.

While such a change could cut donations to all kinds of charities — from food banks to homeless shelters to health clinics — arts groups are feeling especially vulnerable these days. Contributions to nonprofit arts organizations fell 2 percent last year even as overall giving rose 3.8 percent, as donors shifted their giving to basic service providers such as those offering health care and nutrition for the poor, according to Giving USA, which tracks philanthropy.

It’s not clear how much money arts groups would lose in donations in such a tax-code change. In fact, some suggest that donors will continue to give money regardless of the tax implications, cushioning any financial blow. The proposal would not affect donations made by people earning less than the proposed income cutoffs.

But Harvard economist Martin Feldstein estimated in 2009 that an identical proposal would reduce overall charitable giving by about 10 percent as people reconsidered the tax implications of their donations. Other donors might stretch out their contributions or delay them.

“We worry a lot [about the deduction proposal] because the amount of government funding is so small,” said Ford Bell, president and chief executive of the American Association of Museums. “When you start tampering with deductibility, it can become the proverbial slippery slope. The cumulative effect could be devastating.”

Institutions such as museums, universities and hospitals that undertake costly projects rely on the largesse of wealthy individuals. Construction of a new wing or the installation of a major exhibit often depends on the generosity of those who would be most affected by Obama’s plan.

Obama has proposed limiting itemized deductions before, including in his past two budgets and to pay for his health-care reform proposal, but the idea was rejected by Republicans amid fierce opposition by charitable organizations.

Fundraisers say any lost bit will hurt at a time when corporate donors are pulling back and government subsidies are under pressure.

“In general, I think it’s fair to say that it’s very difficult to continually find contributed income in support of the arts,” said Marie Mattson, vice president of development for the Kennedy Center. “It’s a very challenging environment already. Whatever happens on the national landscape that limits that income is problematic for sure.”

Donations comprised about 40 percent of the Kennedy Center’s annual income of $175 million last year.

Some aspects of the president’s jobs bill may actually turn out to be positive for arts organizations, said Robert L. Lynch, president and chief executive of Americans for the Arts, a nonprofit development organization.

Among others, he cited the proposed cut in the payroll tax, which could spur hiring within arts organizations and free up additional spending money; more federal support of schools, which could lead to the hiring and rehiring of arts-education teachers; and more spending on infrastructure projects, which could create more public art projects.

“There are some benefits here,” he said.

The aim of the jobs proposal — getting people back to work and lifting the economy out of another recession — would, of course, be very good for arts organizations, too.

On the other hand, Lynch’s group has some immediate concerns. It has estimated that direct and indirect spending on the arts — from ticket purchases to taxi rides to a show — supported about 5.7 million jobs, and “any less investment in the arts is not good for the economy in general. . . . We don’t think this particular change is as valuable in the money that it saves and raises versus [what it will cost in contributions]. The economy is made better by more money flowing into the American arts economy” than flowing out of it.