As the final minutes of 2012 ticked away and the “fiscal cliff” drew near, some very wealthy philanthropists scrambled to make large, last-minute charitable donations to take advantage of current tax breaks. Less-monied donors and nonprofit groups, meanwhile, worried how the economic uncertainty would affect their bottom line.

With little resolved on Capitol Hill, affluent donors faced a year-end dilemma: should they give more in 2012, or take their chances on what Congress decides to do for 2013?

Would lawmakers tinker with the long-standing charitable deduction? Raise the estate tax? And where would tax rates end up?

It was all so unclear.

In his suburban Maryland office, tax attorney Steve Jacobson worked late Monday while keeping an eye on the cliff debate on CNN. He joked that he was taking a stack of envelopes to a New Year’s party later to dole out to friends. He said they would be monitoring the drama between canapés and, depending on what was decided, might mail off one more big charitable donation just before midnight.

In the end the clock ran out. Jacobson, 54, of Rockville, hedged his bets by doubling the amount of money he put into his personal philanthropic fund — money that will ultimately go to his favorite social-service causes and his alma mater, the University of North Carolina.

“The uncertainty clearly had the effect of getting many ordinarily generous taxpayers to accelerate their giving to some extent,” he said.

Experts said that overall charitable giving is on the rise this year over last but it was too early to say whether the last-minute shenanigans on the Hill would have a major impact on the year’s total — driven up by last-minute donors or down by others who held back because they’re worried about the economic climate. Americans donated nearly $300 billion to charity last year.

“Some people have accelerated their giving and are giving more, ready to get that tax deduction right away and lock it in,” said Stacy Palmer, the editor of the Chronicle of Philanthropy. “Other people are saying it’s better to do it next year. . . . It’s quite split.”

Palmer said some wealthier donors gave bigger gifts toward the end of the year knowing their tax rates were likely to increase and that Congress might change or cap the amount of charitable deductions allowed in the coming year or change the estate tax. Three of the largest charitable gifts this year came in December — Facebook’s Mark Zuckerberg’s nearly $500 million gift to a Silicon Valley community foundation, publisher Mort Zuckerman’s $200 million to Columbia University and Hollywood mogul David Geffen’s $100 million for medical scholarships — although Palmer notes they were likely long-planned.

Under the current terms of the New Year’s deal, the country’s wealthiest Americans — families making $450,000 a year and $400,000 for individuals — will see their tax rates rise and those making over $300,000 will face some limits on itemized deductions. The tax exemption for estates up to $5 million will stay, but tax rates for larger estates will rise from 35 to 40 percent.

The story may be different for less affluent donors. Tim Delaney, the president and CEO of the National Council of Nonprofits, said that the fiscal cliff drama had the potential to rattle the confidence of modest givers who already spent less during the Christmas holidays than expected.

Amanda Andere, the executive director of FACETS in Fairfax, a group that serves the homeless, agreed. She said that her group had already been affected by cutbacks in federal spending, hearing from both individual donors and companies involved in government contracting that they could not give as much this year because they expected rocky times ahead.

The charity had fewer donors this year than last but collected about the same amount of money, Andere said.

“It’s uncertainty of the economic climate,” she said. “People don’t know what’s going to happen next year and whether they can give to as many nonprofits as much as they have given before.”

Some charities and large institutions, such as the Kennedy Center for the Performing Arts, say they are seeing a rise in large donations beyond the normal year-end flurry, when typically a third of giving occurs.

Many of the largest gifts went to so-called “donor-advised” funds, which allow a donor to set up a charitable account and take an immediate tax benefit, and then decide over time how to distribute the money. Financial institutions such as Schwab and Fidelity, which run such accounts, saw big increases as December waned; contributions to Schwab were up 192 percent this December over last. The Jewish Federations of North America, a group that maintains about $10 billion in donor-advised funds, also saw an increase; one federation in New Jersey had 10 seven-figure funds established just in the past week, it said.

Eileen R. Heisman, chief executive of the National Philanthropic Trust, said that giving to its donor-advised funds increased 40 percent in October, 180 percent in November and 300 percent in December. The Pennsylvania-based trust has assets of $1.4 billion.

“I’ve been in this business 25 years and it’s probably the busiest giving season I’ve seen,” she said. “It’s huge.”

With deal terms changing daily, and then hourly, and no closure from Capitol Hill, many taxpayers were left to muddle it out as best they could on their own.

Katherine Borsecnik, 53, a Chevy Chase resident and former technology and nonprofit executive, said that she sat down over dinner just before Christmas with her husband and two daughters, ages 16 and 19, to decide how much they should give to their small family foundation and how the money should be disbursed. The youngest, Lucie, 16, even made her own PowerPoint presentation to argue for her pet causes.

Because they did not know whether they would still have the same charitable deduction next year that they had in 2012, Borsecnik said the family ultimately decided to double their contribution. They selected a variety of beneficiaries from Refugees International to a nonprofit bank in Cambridge.

“This year we stretched more,” she said. “We increased our giving partly because we’ve had a good year and partly because who knows what’s going to happen next year?”