Instead of directly vetting the script he would read for the Guard segment, Mr. Rather says, he acceded to pressure from Mr. Heyward to focus instead on his reporting from Florida on Hurricane Frances, and on Bill Clinton’s heart surgery.

Mr. Rather says in the filing that he allowed himself to be reduced to little more than a patsy in the furor that followed, after CBS — and later the outside panel it commissioned — concluded that the report was based on documents that could not be authenticated. Under pressure, Mr. Rather says, he delivered a public apology on his newscast on Sept. 20, 2004 — written not by him but by a CBS corporate publicist — “despite his own personal feelings that no public apology from him was warranted.”

He now leads a weekly news program on HDNet — an obscure cable channel in which he is seen by only a small fraction of the millions of viewers who once turned to him in his heyday to receive the news of the day.

In filing his suit now — three years after the now-disputed report was first broadcast, and more than a year after he reluctantly left CBS, as his last contract wound down — Mr. Rather is following, by a matter of weeks, the announcement by CBS that it had settled a similar lawsuit by Don Imus.

Mr. Imus had sued CBS over his firing in the aftermath of derogatory remarks he made about the Rutgers University women’s basketball team. While some Imus associates suggested last month that his final payment was at least $20 million, CBS Radio has characterized that figure as too high.

Mr. Rather’s suit seeks $20 million in compensatory damages and $50 million in punitive damages.

Among the pivotal points of contention in Mr. Rather’s suit are the definitions of the words “full-time” and “regular.” As quoted in the filing, Mr. Rather’s contract — which he signed in 2002, and which called for him to be paid a base salary of $6 million a year as anchor — entitled him to a job as a “full-time correspondent” with “first billing” on the midweek edition of “60 Minutes,” should he leave the anchor chair before March 2006, his 25th anniversary in the job.

As it turned out, Mr. Rather would leave the anchor chair a year early, and would indeed be reassigned to the midweek edition, known as “60 Minutes II.” When that broadcast was canceled a few months later, Mr. Rather’s contract called for him to be reassigned to the main “60 Minutes” broadcast on Sunday evening, where he would “perform services on a regular basis as a correspondent.”