The Reagan administration said yesterday it has reduced the flow of new federal regulations by a third since taking office and has cut back on red tape and paperwork so much that its actions will save American producers and consumers more than $70 billion over the next decade.

"Estimating savings is not an easy decision, but we believe these are minimum figures," said Christopher DeMuth, executive director of the Presidential Task Force on Regulatory Relief.

Issuing its fourth "hit list" of regulations which officials hope to relax, Reagan's top regulatory advisers said they already have eased the government's regulatory burden on businesses and state and local governments.

The new hit list of eight regulations is designed to give state and local governments greater flexibility in setting clean air standards, in developing land in floodplains and in having a greater say in the saving or destruction of historic buildings. (Details Page A17.)

The list is the fourth issued by the administration, which already has targeted another 111 rules for review--of which 51 already have been revised or dropped. No more lists are anticipated.

"We think we are making very good progress," said DeMuth.

DeMuth said the administration's regulatory relief actions to date have resulted in a savings of $9 billion to $11 billion in one-time capital investment costs, with an additional annual savings of $6 billion to $6.2 billion.

These figures represent "only a portion of our cost savings" because they apply to less than half of the actions the administration has taken to date, DeMuth said.

Among the greatest beneficiaries, the adminstration said, were state and local governments which have saved $4.1 billion to $6.1 billion in one-time capital investment costs and an additonal yearly savings of $2 billion.

Even more savings are expected, officials noted, once the reviews of all 119 designated rules are completed.

However, in some cases, these figures do not include the benefits that the American public may have lost because of changes of the regulations.

In many instances, officials contend the public lost few, if any, benefits. They gave as an example their relaxation of a rule that would have required New York to spend billions of dollars to refit its subway system for the handicapped. The city still will be required to transport the handicapped--in buses or special taxi services--so few handicapped people will suffer, officials said.

On top of monetary savings, the administration also said it has substantially cut the paperwork burden imposed by the government--by more than 200 million hours.

It said it has cut the number of new rules by one half and the number of pages in the Federal Register--the daily digest of government rules--by one-third.

"The number of final regulations issued by the Reagan administration is about 22 percent less than during the final year of the Carter administration--from a monthly average of 669 during the last year of the Carter administration to 519 during the first 17 months of the Reagan administration," said a fact sheet released yesterday.

What's more, the fact sheet said, the number of proposed rules declined even more sharply--by 34 percent from 460 a month during the last year of the Carter administration to an avearge 302 a month during the first 17 months of the Reagan administration.

"Of course many of the proposed and final regulations issued by the Reagan administration have been to revise rules alerady on the books, rather than to add new ones," the fact sheet said.

Business groups hailed the administration's actions. Yet, as James Carty, vice president and manager of governement relations for the National Association of Manufacturers noted yesterday, business groups are unhappy with administration efforts to get Congress to approve comprehensive regulatory reform legislation.