The United States must accept the inevitable decline of cities in the Northeast and Midwest and adopt a radically new urban policy that encourages people to move to the expanding Sun Belt, says the draft report of the President's Commission for a National Agenda for the Eighties.

The recommendation, which acknowledges the "traumatic consequences" for northern cities, is one of several controversial proposals contained in the report, a copy of which was obtained by The Washington Post.

Other proposals include:

A voucher system that would let people purchase their own health insurance rather than creating a comprehensive national health insurance program.

Encouraging the use of "information disclosure" as an alternative to health and safety regulation.

Economic policies designed to reduce government interference with business to create a "climate in which the private sector can move toward greater rates of growth and productivity."

A negative income tax to replace the welfare system.

Providing industry with more flexibility in meeting environmental regulations, rather than having the federal government determine how standards should be met.

Much of the document has a decidedly antigovernment tone and is likely to be received sympathetically both by the incoming Reagan administration, whose political base is in the Sun Belt, and in the conservative 97th Congress.

The urban policy recommendations promise to be the most controversial. For years, national urban policy has been to create jobs in big cities in the Northeast and Midwest that were suffering from a loss of industry and population to the Sun Belt.

Preliminary 1980 Census Bureau figures show how dramatic that migration has been. San Jose, Calif., Phoenix, Ariz., El Paso, Tex., Houston and San Diego each grew by at least 20 percent over 10 years. Major cities that lost at least 10 percent included Chicago, Philadelphia, Detroit, Baltimore, Milwaukee, Cleveland, Boston, Pittsburgh and Washington.

"We cannot . . . avoid the fact that growth and decline are integral parts of the same dynamic process in urban life," the report says. "When the federal government steps in to try to alter these dynamics, it generates a flood of demands that may sap the initiative of urban governments via the expectation of continuing support. There must be a better way.

"There is a fundamental problem in attempting to halt the shrinkage of metropolitan areas or the revitalization of obsolete industries which in the past have been expected to adapt themselves to changing circumstances. In our view the moral and material resources of government would be better expended in planning for the future and helping people to adjust to future imperatives in ways that derive from an understanding and acceptance of change."

The commission specifically recommends more emphasis on retraining and relocation assistance, cash help for people who cannot work as well as the "working poor," and subsidies to private employers "to ensure that jobs created by government are only temporary and supplemental bridges to eventual employment in the private sector."

The commission recognizes the "traumatic consequences for a score of our struggling largest and oldest cities" and urges programs that alleviate some of the financial burdens on those cities, particularly the cost of welfare.

"This transformation of older cities, from centers of manufacturing and production to centers of services and consumption will require that their 'health' be defined at new, and often lower, levels of population and employment," the report says.

At the same time, the commission recognizes that regional warfare has made it difficult for the federal government to devise acceptable policies in many areas and urges a greater role for political institutions and parties in resolving these conflicts.

On health care, the commission argues that federal programs are "the worst of two worlds" and says an expansion of "competition, consumer choice and market incentives, rather than government control" would provide a better and cheaper national system.

The proposals on health, safety and environmental regulations grow out of a feeling by commission members that the federal role here is likely to undergo "a searching reexamination" in the 1980s.