Google Tuesday began to fill in the picture on how it plans to offer application services to enterprise customers when it introduced Google Apps for Education, a collection of collaboration tools and an API set for backend integration.

Google also announced that Arizona State University is converting 65,000 users to the Google Apps platform and that the school has already used the Google APIs to integrate its infrastructure, including its e-mail gateway.

Google Apps for Education is a derivative of Google Apps for Your Domain, which was introduced in August. The education version contains Gmail, Google Talk and Google Calendar. The online service requires only a Web browser client.

The unique aspect of the education version is a set of APIs that lets users tie the Google services to existing backend infrastructure such as directories and single sign-on platforms. Google is using standards such as the Security Assertion Markup Language to support single sign-on and a Representational State Transfer (REST)-based XML interface to link to directory services.

The API set is a hint at what Google plans to offer corporate users when it introduces an enterprise edition of Google Apps before the end of the year.

“These are the kinds of things we are thinking about for the enterprise edition,” says Rajen Sheth, product manager for Google Apps for Education. “Integration like this is what will be important for the enterprise edition as well.”

Google plans to offer versions of Google Apps for Your Domain designed for specific organizations such as non-profits, large companies, and ISPs.

A premium version of Google Apps, which will not include advertising, is slated for beta later this year for users “with more advanced needs.” While Google has not provided specifics it said the premium service would be fee-based and include specific service level and support agreements. Those agreements also are likely to be part of a package of services offered to corporate users.

Experts have said that a major challenge for Google offering corporate services would be developing service-level agreements (SLA) for hosted services.

Google says that thousands of universities are part of its Google Apps for Your Domain beta and that ASU is the first major university to convert its users and develop integration using the Google API set.