For some people, the warm feeling they get all over when they write the check is enough. But many others need an additional incentive to make a donation to their favorite charity, particularly if they are in a high income-tax bracket.
Until this year, those in a plus-50 percent tax bracket knew they could deduct over half of their donation on their federal tax forms. But after the Reagan tax cuts went into effect there was no bracket higher than 50 percent any more. And many of the charities that traditionally depend on generosity of upper-income people expressed concern that they would lose out.
While it is too early to tell if there is any foundation to the charities' fears, George Pillsbury believes well-heeled people can still find ways to make charitable contributions and deduct more of the donation than they may have thought possible.
Mr. Pillsbury is a consultant with the Funding Exchange, a national organization of seven community-based foundations. He recently helped prepare a booklet on charitable giving: ''Gift Giving Guide: Methods and Tax Implications of Giving Away Money.''
Instead of just sending in that check, Mr. Pillsbury says, upper-income people should do more planning to find some less-conventional ways to make a donation:
* Consider giving away stock. If you have held the shares more than one year and then give them to a qualified charity, neither you nor the charity would have to pay taxes on the long-term gain that would have been subject to tax. You would also be able to deduct the value of the stock at the time you made the donation.
* If you think you will need additional deductions this year, consider deferred giving. You are simply saying that the charitable organization will receive so much money at a particular time, possibly at your passing, or after a specific number of years. While this commitment is irrevocable, it does give you an immediate deduction, and you get to keep any additional capital or interest the money may earn before it is turned over to the charity's control.
* Remember the five-year carryover. If a person uses part of their capital to make more donations than usual, the contributions may exceed 50 percent of their adjusted gross income. But the IRS won't allow you to deduct any contributions that exceed 50 percent of your income. In this case you can ''carry over'' the excess donations and spread the deductions over all or part of the next five years.
* Just because you don't know what charity you want to give money to, don't let that stop you from making a donation. This might sound impossible, or even unnecessary, but people often want to gain the tax advantage of a donation before they have a recipient in mind. In this case, you can give the money to a ''donor-advised fund.'' These are organizations or public foundations set up to help fund a variety of charities and other nonprofit organizations. They usually have certain types of organizations they favor, but you can make the donation to the fund and designate exactly where it is to go later.
* If you are considering giving money through your will, you might want to think about making a cash gift now instead, since your heirs can get a larger portion of your estate tax-free under the new law.
There are a number of other ideas on charitable giving in the 58-page booklet , which is available for $6.50 from the Funding Exchange, 80 Fifth Avenue, Room 1204, New York, N.Y. 10011.