The National Association of Manufacturers yesterday gave the Reagan administration a grade of B-minus for its regulatory reform efforts and warned that the momentum for change "is slowing down."

"Regulatory reform is not moving in any significant way at the present time," Jerry J. Jasinowski, the NAM's senior vice president and chief economist, told a breakfast meeting of reporters.

He blamed the Reagan White House for failing to push legislation that would solidify gains achieved through executive orders "that moved us one-third of the way down the road to reasonably comprehensive regulatory reform."

As a result of the failure to get these major changes in administrative procedures enacted into law, "there is a substantial chance they could be watered down" by a new administration that would overturn the Reagan executive orders, Jasinowski continued. But he said he doubts that the changes would be "completely vitiated."

Jasinowski said the Reagan administration did not assign the same priority to regulatory reform that it did to budget and tax cuts and national security. He said the business community assumed there was no need to apply pressure on government with Republicans in power.

At the same time, Jasinowski said that Congress has not faced up to the problems created by the host of regulatory laws passed in the 1970s, and that the proponents of strong government regulation "have been opposed to any meaningful change, and that is part of the problem."

In many ways, the NAM's analysis of the Reagan administration's failure to push regulatory reform far enough parallels one issued almost a year ago by the Heritage Foundation, a conservative think tank..

Jasinowski said the NAM still hopes to get action on seven regulatory reform laws in the current Congress even though it will be an election year, when it is often hard to win approval of major legislative changes. The NAM's legislative agenda includes:

* Decontrol of natural gas.

* Enactment of an omnibus regulatory reform bill that would lock into law many of the Reagan administrative changes.

* Changes in the clean water act.

* Continued authorization of the Federal Trade Commission with a tighter definition of what constitutes unfairness to the consumer and a new form of congressional veto over agency actions.

* Continued deregulation of the trucking industry through the removal of antitrust immunity for rate setting.

* Enactment of a federal product liability law.

Jasinowski insisted the business community believes regulation and economic growth can go together, but merely wants to reform current regulatory laws to make them work more efficiently.

He listed the overall cost of regulation to the American economy at $145 billion a year--a figure based largely on a study made by the former chairman of Reagan's Council of Economic Advisers, Murray Weidenbaum. This figure has been sharply criticized as inaccurate by Ralph Nader's Public Citizen organization.

Under questioning, Jasinowski acknowledged that regulation had produced benefits for the American economy, but he said the NAM never has tried to quantify the amount and compare it with the costs.

Joan Claybrook of Public Citizen cited two studies to illustrate the economic and social benefits of regulation. One, by Yale professor William Nordhause, found the refusal to go ahead with air bag and seat belt laws cost the economy $2.4 billion a year. Another, published by the Transportation Department last May, found each dollar spent on a car for auto safety prevents 27 deaths. Claybrook said that is the equivalent of 10,000 lives saved each year because of auto safety regulations.

Jasinowski defended using the $145 billion cost figure as "setting the stage for the need to achieve these benefits at a lower cost."

The NAM chief economist also agreed that the current fast-paced deregulation of banks and savings and loan institutions has placed extra costs on the economy. Financial institutions have raised interest rates they charge borrowers because, in order to compete for savings, they have lost the benefits of low-interest passbook savings accounts that once fed their profits. He estimated that added about 1 percent to the country's already bloated interest rates.