If doing your bit for charity means dropping a few coins in a hat, then the Funding Exchange's new how-to booklet is not for you.

But if your idea of generosity is 25 bucks or even $10,000, the community-activist organization's Gift-Giving Guide: Methods and Tax Implications of Giving Away Money could be a help. Its purpose is to help donors--and recipients--get the most out of money by taking advantage of tax laws. Or, as the guide points out, there is "a financial as well as a philosophical rationale for giving money to charitable organizations."

From simple cash gifts, the guide goes on to explain such sophisticated techniques as "charitable lead trusts" and "deferred-giving" plans utilized by the wealthy. It even gets into the nitty-gritty of how to will money to a lover (gay or otherwise) to fend off challenges from family members.

"Make that person the executor of your will," advises the 60-page guide. While this technique isn't foolproof, "it does put your loved one in a strong position."

The Funding Exchange is an umbrella organization for seven public foundations throughout the country. The Washington group is Common Capital Fund, whose office is located above an auto-supplies store at 18th Street and Columbia Road NW.

The D.C. foundation solicits donations for "community social-change projects that might have difficulty getting money from other sources," says executive director Phyllis Jones.

In 1981, the fund's first year, it gave $30,000 (received mostly from individual contributors) to 22 Washington groups out of more than 200 applicants. It wants to increase that amount to $60,000 this year.

To date, the primary focus has been on Hispanic issues, housing and women's rights.

The Funding Exchange emerged from the ranks of the anti-Vietnam war and civil-rights activists of the '70s, says Jones, and has been financed in large part by "individuals with inherited wealth." The organization now is trying to broaden its base to include less well-heeled supporters, which was the purpose of producing the guide.

While the obvious hope is that Funding Exchange's member groups will capture a good share of any resulting donations, the book's advice is applicable to any gift-giving.

Among the guide's suggestions:

* Consider giving stock instead of cash. On appreciated property, you receive a double benefit: "avoiding taxes on capital gains and getting your regular charitable deduction for the full value of the gift."

An example: You buy 100 shares of stock for $4 (cost $400). The stock appreciates to $12 a share (now worth $1,200). If you keep it, you pay taxes on a percentage of the capital gains ($800). If you give the stock away, neither you nor the charity must pay, and you take a $1,200 deduction.

* If you do not itemize on your income taxes, take advantage of a provision in the 1981 Tax Act that permits you to take a charitable deduction in the years 1982-86. Initially, the ceiling is $100 on such a contribution (with a maximum deduction of $25). But by 1986, you can donate as much as you want and take a full deduction for it.

* Make your support in the form of an interest-free loan, to a group, for example, awaiting a grant. Or cosign a mortgage for a nonprofit organization buying a house or building.

To obtain a copy of the Gift-Giving Guide, send $6.50 (plus $1 postage) to Common Capital Fund, 2451 18th St. NW, Washington, D.C. 20009. The book is free with a $100 contribution.