President Carter sent his long-awaited plan for the overhaul and increased funding of public broadcasting to Congress yesterday, calling for a five-year, $1 billion authorization starting in fiscal 1981.

In his accompanying message, Carter emphasized that his proposals "will also increase public broadcasting's insulation from inappropriate political influence."

That comment and his stress on increased programming independence for the public system seemed to signal the end of the creative and journalistic strictures which many believe were placed on public broadcasting during the Nixon administration.

"Because it is free of the scramble for ratings," the President said, "public broadcasting has room for ex-perimentation and risk-taking . . . to meet the needs of audiences that number in the millions but are seldom served anywhere else."

Citing his plans for long-term federal funding and a reduction of the "overlap" of the missions of the Corporation for Public Broadcasting, the Public Broadcasting Service and National Public Radio, Carter said:

"The changes will also increase public broadcasting's insulation from inappropriate political influence. Other amendments (to the Public Broadcasting Act of 1967) will give it greater journalistic independence. I want to encourage public broadcasters at all levels to engage in active news reporting and public affairs programming.

"This administration," Carter continued, "will not try to stifle controversy on public television and radio."

During the Nixon administration, critics charged that CPB, established in 1967 as a non-political "buffer" between Congress and the public systems, used its role as a conduit of federal money to TV and radio to limit controversial and/or public affairs programming which the Nixon White House disliked.

In addition to a call for more programming independence, Carter's proposed legislation stresses greater participation by minorities and women, more system accountability to the public and bigger audiences for the system's stations through improved signals and equipment.

The White House plan calls for financial stability bolstered by a five-year, $1.04-billion authorization, including $180 million in fiscal 1981 and $200 million for each of the four years thereafter.

In addition, the Carter plan would double to $30 million annually, funding for improved equipment at the 271 TV and 203 radio stations currently in the system.

At the same time, the administration asked Congress to increase the percentage of federal funds available for national programming to approximately $50 million a year, or 25 per cent of the annual funding, up from a current 17 per cent. With station contributions, an estimated $100 million would be available each year. The plan gives the Public Broadcasting Service control of national programming, which in recent years has been mostly in the hands of CPB.

Moreover, the President calls for a "substantial" reduction in the current 130-member staff of the Corporation for Public Broadcasting, particularly in the areas of legal, public information and audience research services. They were cited yesterday as examples of program-related functions that would become unnecessary as PBS and National Public Radio assume programming functions now controlled by CPB.

The Carter package would strengthen use of current employment discrimination laws as they apply to stations and other producers in and out of the public system to guarantee more minority participation.

The bill snet to Congress yesterday also asks better reception standards for public TV and radio, which currently reach only 50 and 60 per cent, respectively, of their potential national audiences.