The U.S. transportation system, beset with problems, would benefit from a set of national guidelines that stress energy conservation, improved maintenance of assets such as the highway system and reliance on an unregulated private sector to meet most needs, a new report says.

The national transportation study was conducted by the National Chamber Foundation, a research organization of the U.S. Chamber of Commerce. Executive Vice President Thomas J. Donahue said the foundation's purpose is to develop a national dialogue on transportation problems in an attempt to bring attention and solutions to them.

The issues are ripe for development. Petroleum costs are soaring, and transportation consumes 50 percent of the petroleum used in the United States. The highways are falling apart, key waterway facilities are in major need of repair, railroads are being forced into bankruptcy, public transit is experiencing enormous deficits and escalating costs and the Reagan administration is talking about cutting federal transportation expenditures.

Those facts have been highlighted in two major studies over the past four years, one by the Department of Transportation, the other by Congress. Both efforts occupy prominent places on the shelves of transportation economists but have caused no perceptible change in national transportation policy.

The Chamber Foundation's effort, much less exhaustive, has the potential for more impact because of substantial participation by the U.S. business community. The study itself will be discussed at a conference beginning today in Florida.

The foundation study proposes 10 national guidelines that emphasize the role of private industry in solving transportation problems."Wherever possible, the provision of transport services should be left to private enterprise functioning in a competitive market, and the costs should be borne directly by the users of the system through free-market prices," according to proposed Guideline Number One.

Only if private industry cannot do the job should government intervene, the study says. And if the government must intervene, it should do it at the most local level possible.

In general the study applauds the trend toward deregulation in transportation that started in the Carter administration and is receiving continued emphasis under President Reagan.

The user-pays concept of transportation financing is totally bipartisan. The problem is that nobody has yet figured out a perfect way to allocate costs to the users. Government always has had to intervene at some point and make an arbitrary decision on that subject.

The Highway Users Federation, a group that has lobbied successfully for highway funds, sponsored the project, but Donahue insisted the federation "didn't buy the study."

Nonetheless, the study makes strong arguments for positions that long have been espoused by prohighway interests: increasing tax spending for road maintenance, abandoning unprofitable railroad lines and eliminating federal dollars for urban mass transit.