THE HAGUE — Secretary of State Hillary Rodham Clinton and other international leaders urged countries and private businesses on Thursday to fight increasing efforts to restrict access to the Internet by repressive governments and even some democratic ones.

Opening a two-day conference on digital freedom here sponsored by Google and the Dutch government, Mrs. Clinton warned that restrictions on the Internet threatened not only basic freedoms and human rights, but also international commerce and the free flow of information that increasingly makes it possible.

“When ideas are blocked, information deleted, conversations stifled and people constrained in their choices, the Internet is diminished for all of us,” Mrs. Clinton said. She added: “There isn’t an economic Internet and a social Internet and a political Internet. There’s just the Internet.”

Mrs. Clinton and others cited examples in which autocratic countries — often with the assistance of international technology corporations — cracked down on access to the Internet or the use of it, including Syria, Iran, China and Russia. But increasingly some democratic countries have tried to restrict information, a development that underscores the complexity of controlling an essential part of modern life.