The Treasury Department yesterday released a detailed study of the value added tax -- a form of national sales tax -- which it estimated could raise billions of dollars in new tax revenue.

Treasury officials said the Reagan administration has no intention of seeking such a tax, but the VAT study was the only alternative offered by the Treasury to the flat tax plan it released several weeks ago.

The value added plan has the strong support of the business community, according to Treasury officials, who said VAT was a close contender to the flat tax among the various tax plans under consideration by the government.

"Having made a major study of it VAT , we felt we may as well publish it just to add to the body of knowledge," Treasury Secretary Donald T. Regan said of the VAT study. "We are not going to be in favor of a VAT."

Earlier this month, however, Regan said that while the administration isn't considering a VAT now, such a tax "might be needed some year, some time in the distant future, if we ever needed to raise taxes."

A VAT is a tax on each level of production of an item for sale. But businesses receive credits for the taxes they pay for products they need during processing, so that by the time the product reaches consumers at the retail level, the VAT acts just like a national sales tax.

The allure of the VAT is that it can raise taxes relatively painlessly. According to the study released yesterday, each percentage point of such a tax would yield $31 billion in revenue in 1988 if no types of purchases were excluded. If certain items were excluded from the tax base for administrative, social policy or other reasons, the tax could raise $24 billion in 1988, the Treasury study said.

Items such as medical care, educational and religious expenses and welfare costs probably would not be taxed for social reasons, the Treasury said. In addition, food eaten at home might be excluded.

The Treasury Department considered the VAT as part of its year-long study of alternative programs to replace the current income tax system. President Reagan, in his State of the Union address in January, asked the Treasury to devise a new tax system that would be fairer and simpler than the current 71-year-old tax program and would promote economic growth without raising new revenue.

Regan proposed last month that the system be changed to a modified flat tax that would trim the number of tax brackets for individuals from about 14 to three and would reduce the maximum tax rate from 50 percent to 35 percent. For corporations, the Treasury plan would reduce the maximum tax rate from 46 percent to a flat 33 percent. Many deductions and exemptions would be eliminated.

The Treasury said in the study released yesterday that it rejected the VAT because it would be regressive -- or would hurt lower-income taxpayers more than the wealthy -- would intrude into the state sales tax area, would provide an incentive for the government to spend more money and would require about $700 million and 20,000 more workers to enforce.

On the plus side, the VAT would not affect savings, investment or consumption decisions, the Treasury study said.

"It's interesting that the Treasury analysis of VAT is as positive as it is, although they rejected it because of the need to come up with a revenue-neutral package," said Jerry Jasinowski, chief economist for the National Association of Manufacturers. The NAM has rejected parts of the Treasury's proposed modified flat-tax plan as being harmful to business.

"It looks like the Treasury could fall back to a VAT option if they had to raise revenues," Jasinowski said. "VAT is going to be a bigger issue next year than people realize" when the deficit debate begins.

However, economist Alan Greenspan, an informal adviser to President Reagan and a former chairman of the Council of Economic Advisers during the Ford administration, said that the VAT study could be used to counter any push for such a tax by businesses during the upcoming debate on tax reform and deficit reduction.

"It's clear that in the context of all the fiscal options in the last few years, VAT . . . is one of the major items which business . . . tends to support" if taxes need to be raised, Greenspan said. "I think the reason they've released it is that it is a significant option of which they disapprove and which they are endeavoring to produce evidence against."

The VAT concept dates from about 1919. However, the first VAT was not adopted until France began a wholesale-level value added tax in 1955. The tax was adopted by Denmark in 1967, Germany and the Netherlands in 1968, Luxembourg in 1970, Belgium in 1971, Ireland in 1972 and Italy and the United Kingdom in 1973. Greece is expected to adopt a VAT by 1986. Austria, Norway and Sweden and many developing nations also have such taxes.

The VAT idea was proposed in the 1970s by Al Ullman, former chairman of the House Ways and Means Committee, whose reelection defeat was blamed at least in part on his espousal of the tax plan for the United States.

According to the Treasury study, revenue from a VAT "could be used to reduce the deficit, to reduce or replace other taxes or to finance increased government spending for defense or social spending."

"Policy makers, therefore, are likely to view the value added tax as a mixed blessing," the study said. "Some may applaud its economic neutrality and its anticipated favorable impact on economic growth and productivity, but be concerned over its potential for funding a permanently higher level of government spending. Others may attempt to balance its regressive aspects with its ability to generate funding for new or expanded government programs."

States and local governments have lobbied against a VAT, saying it would encroach on their tax base since many of them depend on sales-type taxes for a large part of their revenue. However, the study said that the federal government should not refrain from adopting a VAT merely because 45 states and the District of Columbia impose sales taxes.

The study said many services would be difficult to include in the VAT base, including health and hospital care, education, and religious and welfare activities.

Farmers and small businesses could be hurt by a VAT because of the administrative problems involved, the study said. The study recommended that if a VAT were ever adopted, small firms should be required to comply, but that street vendor-type businesses or those making casual sales be exempt from registration. The study also recommended exempting farmers.