One group that at least skates close to the line is Friends of Zo Artzeinu/Manhigut Yehudit, based in Cedarhurst, N.Y., and co-founded by Shmuel Sackett, a former executive director of the banned Israeli political party Kahane Chai. Records from the group say a portion of the $5.2 million it has collected over the last few years has gone to the Israeli “community facilities” of Manhigut Yehudit, a hard-right faction of Mr. Netanyahu’s governing Likud Party, which Mr. Sackett helps run with the politician Moshe Feiglin.

American tax rules prohibit the use of charitable funds for political purposes at home or abroad. Neither man would answer questions about the nature of the “community facilities.” In an e-mail message, Mr. Sackett said the American charity was not devoted to political activity, but to humanitarian projects and “educating the public about the need for authentic Jewish leadership in Israel.”

Of course, groups in the pro-settler camp are not the only ones benefiting from tax breaks. For example, the Free Gaza Movement, which organized the flotilla seeking to break Israel’s blockade of Gaza, says on its Web site that supporters can make tax-deductible donations to it through the American Educational Trust, publisher of an Arab-oriented journal. Israeli civil and human rights groups like Peace Now, which are often accused of having a blatant political agenda, also benefit from tax-deductible donations.

Some pro-settler charities have obscured their true intentions.

Take the Capital Athletic Foundation, run by the disgraced Washington lobbyist Jack Abramoff. In its I.R.S. filings, the foundation noted donations totaling more than $140,000 to Kollel Ohel Tiferet, a religious study group in Israel, for “educational and athletic” purposes. In reality, a study group member was using the money to finance a paramilitary operation in the Beitar Illit settlement, according to documents in a Senate investigation of Mr. Abramoff, who pleaded guilty in 2006 to defrauding clients and bribing public officials.

Mr. Abramoff, documents show, had directed the settler, Shmuel Ben Zvi, an old high school friend, to use the study group as cover after his accountant complained that money for sniper equipment and a jeep “don’t look good” in terms of complying with the foundation’s tax-exempt status.

While the donations by Mr. Abramoff’s charity were elaborately disguised — the group shipped a camouflage sniper suit in a box labeled “Grandmother Tree Costume for the play Pocahontas” — other groups are more open. Amitz Rescue & Security, which has raised money through two Brooklyn nonprofits, trains and equips guard units for settlements. Its Web site encourages donors to “send a tax-deductible check” for night-vision binoculars, bulletproof vehicles and guard dogs.

Other groups urge donors to give to one of several nonprofits that serve as clearinghouses for donations to a wide array of groups in Israel and the West Bank, which, if not done properly, can skirt the intent of American tax rules.