CBS News employees repped by the WGA have ratified a three-year deal with the network with 98% backing.

The pact, which covers about 500 employees, ends a three-year battle. The previous contract expired in April 2005.

The guild and CBS reached a tentative deal two weeks ago — two months after the WGA’s CBS News members backed a strike authorization with 81% support. The prospect of a picket by network employees forced the Democratic National Committee to cancel last month’s presidential debate set for L.A. for broadcast on CBS.

Before the agreement was reached, the WGA had insisted that CBS drop its demand to create a two-tiered work force by paying lower salary increases to local radio employees. It also wanted CBS to back off its demand for the right to assign current WGA responsibilities at KNX Radio in Los Angeles to non-WGA employees.

The contract goes into effect immediately and covers newswriters, editors, news desk associates, production assistants, graphic artists, promotion writers and researchers working in national and local TV and radio in New York, Chicago, Los Angeles and Washington, D.C. The vote was held at special meetings in those cities earlier this week.

Terms call for a 3.5% raise immediately and another in a year. In addition, most regularly scheduled employees who worked 200 days or more in 2007 and did not get wage increases during the negotiations will receive an extra $3,700. Employees who worked shorter schedules will receive pro-rated payments.

The contract runs through April 1, 2010.

“This very-difficult-to-achieve contract is the product of a long mobilization effort by the guild’s members working at CBS,” said Mona Mangan, exec director of the WGA East. “This strong vote of approval signals their commitment to a contract that is free of the rollbacks that members so strongly opposed. Our members look forward to a renewed commitment to quality news during an exciting presidential election year.”