WASHINGTON — As Senators McCain and Obama intensify their battle for the White House, they are scrutinizing their own campaigns to purge them of the taint of lobbyists and their big-bucks clients.

But the strategists behind those efforts are senior aides with a more-than-passing resemblance to — what else? — lobbyists.

Mr. Obama is well ahead of Mr. McCain in restricting lobbyist participation. But the history of both candidates is peppered with campaign operatives, policy advisers, and others who have clear links to the longstanding but often scandal-tinged practice of making money by trying to influence politicians.

The campaigns have begun attacking each other about lobbyist ties — and who is doing the most to limit them — following the resignation of several senior McCain advisers in the past two weeks because of lobbying involvements, including work for foreign regimes.

Two McCain staffers who in the past have lobbied on behalf of controversial foreign clients are leading the high-profile drive to rid his campaign of lobbyists. And Mr. Obama’s reformer image has been fostered in part by a Chicago political consultant with a sideline in so-called grass-roots lobbying for corporate clients — although he vehemently denies being a lobbyist and says he never approached or provided access to an officeholder.

Both candidates can boast of genuine accomplishments in passing ethics reform legislation. Yet the challenge they face in separating their campaigns from lobbyists illustrates how difficult it is for any ambitious politician to declare independence from Washington’s K Street culture and the economic interests that underlie it. That’s especially true of politicians seeking the White House. After all, it’s the lobbying companies and related enterprises that know how to run a high-tech voter mobilization drive, develop a hard-hitting radio spot, and, most important, raise the millions of dollars necessary to wage a strong campaign.

The revolving door connecting politics and interest-group advocacy is a Washington institution. For aspiring Democrats and Republicans alike, serving as a senior aide to a prominent politician is one of the main career paths for a lucrative career in lobbying — and vice versa.