REAL INSIDERS.(United States foreign relations)

Several years ago, I had dinner at Galileo, a Washington restaurant, with Steven Rosen, who was then the director of foreign-policy issues at the American Israel Public Affairs Committee. The group, which is better known by its acronym, aipac, lobbies for Israel's financial and physical security. Like many lobbyists, Rosen cultivated reporters, hoping to influence their writing while keeping his name out of print. He is a voluble man, and liked to demonstrate his erudition and dispense aphorisms. One that he often repeated could serve as the credo of K Street, the Rodeo Drive of Washington's influence industry: "A lobby is like a night flower: it thrives in the dark and dies in the sun."

Lobbyists tend to believe that legislators are susceptible to persuasion in ways that executive-branch bureaucrats are not, and before Rosen came to aipac, in 1982 (he had been at the rand Corporation, the defense-oriented think tank), the group focussed mainly on Congress. But Rosen arrived brandishing a new idea: that the organization could influence the outcome of policy disputes within the executive branch--in particular, the Pentagon, the State Department, and the National Security Council.

Rosen began to court officials. He traded in gossip and speculation, and his reports to aipac's leaders helped them track currents in Middle East policymaking before those currents coalesced into executive orders. Rosen also used his contacts to carry aipac's agenda to the White House. An early success came in 1983, when he helped lobby for a strategic cooperation agreement between Israel and the United States, which was signed over the objections of Caspar Weinberger, the Secretary of Defense, and which led to a new level of intelligence sharing and military sales.

aipac is a leviathan among lobbies, as influential in its sphere as the National Rifle Association and the American Association of Retired Persons are in theirs, although it is, by comparison, much smaller. (aipac has about a hundred thousand members, the N.R.A. more than four million.) President Bush, speaking at the annual aipac conference in May of 2004, said, "You've always understood and warned against the evil ambition of terrorism and their networks. In a dangerous new century, your work is more vital than ever." aipac is unique in the top tier of lobbies because its concerns are the economic health and security of a foreign nation, and because its members are drawn almost entirely from a single ethnic group.

aipac's professional staff--it employs about a hundred people at its headquarters, two blocks from the Capitol--analyzes congressional voting records and shares the results with its members, who can then contribute money to candidates directly or to a network of proIsrael political-action committees. The Center for Responsive Politics, a public-policy group, estimates that between 1990 and 2004 these pacs gave candidates and parties more than twenty million dollars.

Robert H. Asher, a former aipac president, told me that the pacs are usually given euphemistic names. "I started a pac called Citizens Concerned for the National Interest," he said. Asher, who is from Chicago, is a retired manufacturer of lamps and shades, and a member of the so-called Gang of Four--former presidents of aipac, who steered the group's policies for more than two decades. (The three others are Larry Weinberg, a California real-estate developer and a former owner of the Portland Trail Blazers; Edward Levy, a construction-materials executive from Detroit; and Mayer "Bubba" Mitchell, a retired builder based in Mobile, Alabama.)

aipac, Asher explained, is loyal to its friends and merciless to its enemies. In 1982, Asher led a campaign to defeat Paul Findley, a Republican congressman from Springfield, Illinois, who once referred to himself as "Yasir Arafat's best friend in Congress," and who later compared Arafat to Gandhi and Martin Luther King, Jr.