The arrest Tuesday of Robert Johnson, the former Newsday publisher and a New York State regent, was one of hundreds so far growing out of a 2 1/2-year-old federal investigation that targets the financing of child pornography Web sites, according to sources familiar with the case.

The arrest Tuesday of Robert Johnson, the former Newsday publisher and a New York State regent, was one of hundreds so far growing out of a 2 1/2-year-old federal investigation that targets the financing of child pornography Web sites, according to sources familiar with the case.

The New Jersey-based probe by U.S. Immigration and Customs Enforcement and the Internal Revenue Service was aimed initially at Regpay, a firm in Minsk, Belarus, in the former Soviet Union, according to the sources and court documents.

Regpay, and several related firms, served as clearinghouses for credit-card payments from purchasers of child pornography to some 50 Web sites around the world, and operated four Web sites on its own that distributed child pornography, according to sources and documents.

The Regpay probe led to convictions against executives of those businesses in Newark federal court. The president of Regpay, Yahour Zalatarou, was lured from Belarus to Paris where he was arrested by immigration agents, and extradited to the United States, where he pleaded guilty earlier this year to distribution of child pornography and money laundering, said sources and court records.

Now in a second phase of the Regpay case, prosecutors have been systematically going after customers, with Johnson, 59, apparently the latest one.