Rep. Paul G. Rogers, a Florida Democrat who has become "Mr. Health" for his backing of major health laws, surprised Congress and his constitutions yesterday by announcing he will not run for reelection.

Now in his 12th term, with no important opposition, Rogers said he merely wants to try to "change of career" age 57, perhaps law, perhaps business or industry or "the private sector."

His retirement will cost the Carter administration one of its stalwarts on health and environment. The announcement came as he was in the midst of trying to get a deeply split Commerce Committee to pass at least some modified form of a hospital cost control plan President Carter has called essential.

Now chairman of that committee's health subcommittee, Rogers sponsored the Clean Air Act of 1970, and laws to strengthen medical research, train health manpower, regulate medical devices, give health services to migrant workers and keep the National Cancer Institute in the National Institutes of Health.

He was first elected in 1955 in a special election after the death of his father, Rep. Dwight L. Rogers. Representing a large slice of Florida that includes much of Palm Beach and Broward counties, he won 91 percent of the vote in his last campaign.

He is "open to offers," he said, and would consider a major government job if one were offered. But first, he said, he wants to help "squeak" hospital cost control through the Commerce Committee and Congress.