President Carter's policy of reducing U.S. arms sales overseas is not likely to bring down the world-wide traffic in conventional weapons - and may not be politically acceptable at home - unless other nations can be persuaded to adopt similar restraints, according to administration documents released yesterday.

"The prospect that other countries will voluntarily and spontaneously follow our model of restraint is unlikely," said a National Security Council study. The study formed part of the basis for Carters May 19 announcement of a more restrictive U.S. policy on the sale of conventional arms abroad. A declassified form of it was transmitted to the Senate Foreign Relations Committee, which made it public yesterday.

The NSC report - and Carter's May 19 announcement - called the new U.S. policy a "first step" in limiting the worldwide conventional arms race. The report went on to say, however, that "it will be difficult to sustain unilateral U.S. restraint over the longer term" if other countries do not follow the U.S. example.

The report named France, Britain, Israel, Germany, Italy, Belgium, Sweden and the Soviet Union as countries which might sell weapons to "determined purchasers" whose arms requests are turned down by the United States.

If such countries rush to fill the vacuum caused by U.S. cutbacks, "the pressures in this country to loosen the bonds of restraint could become substantial," the report said.

According to Central Intelligence Agency data published in the report, the United States accounted for more than half of the worldwide arms traffic to developing nations in recent years, calculated on a dollar basis, With 56 per cent of the sales, the U.S. share is more than twice that of other non-Communist suppliers combined (26 per cent) and more than three times the sales of the Soviet Union and other Communist suppliers (18 per cent) and more than three times the sales of the Soviet Union and other Communist suppliers (18 per cent).

About 52 per cent of U.S. government-to-goverment sales are to three Middle Eastern countries - Saudi Arabia, Iran and Israel. South Korea, Australia and Jordan are listed as the next largest arms purchasers from the United States.

ON the other hand, the Soviet Union is the dorminant supplier to Africa and South Asia, a major supplier to the Middle East and ranks ahead of the United States as an arms supplier to Latin America, the report said.

Though the past, U.S. reluctance to sell arms to Africa and Latin America may have had "some dampening effect," has probably been to transfer business to other arms supplier. The United States has only a minor role in providing arms to Africa and is behind Italy and Britain as well as the Latin America, according to the study.

Arms purchases by developing countries from all sources have begun to decline since the 1974 peaks of $21 billion, the study said. The reduction was 20 per cent in 1975 and another 15 per cent last year. "Unless major potilitical, economic or military developments upsets this trend, the CIA projects that worldwide new orders may level off at $10 billion-$15 billion anually by 1980," the study said.

Congress in controversial actions has set arms policy by legislating anban on U.S. sales to Chile and Urguay because of human rights violations and by enacting restrictions on sales to Turkey due to misuse of U.S. arms in the Cyprus invasion.

The Ford administration persuaded Congress to permit Turkey to purchase up to $125 million of U.S. arms in fisca1 year 1976 and 1977 in order to forestall a further deterioration of relations with that NATO ally.

According to informed sources the Defense Department recently informed members of Congress that Turkey may have exceeded the 1976 ceiling by purchasing $30 million in U.S. missiles, aircraft engines and helicopters from a NATO maintenance and supply organization located in Luxembourg.

A Pentagon spokesman said yesterday a study is under way of the Turkish puchases from the NATO group. The spokesman would not say, in response to questions, who was responsible for the apparent violation of the limit imposed by Congress.

In an effort to win the cooperation of European weapons supplier with his drive for worldwide restraint, Carter discussed his new arms export policies with heads of government during the recent London summit meeting. U.S. officials said diplomatic discussions with European governments are taking place in hopes of obtaining their agreement to cut back sales.

However, overseas arms sales are an important economic prop for some of the countries involved and officials conceded that government would not be easy.

The United States and the Soviet Union agreed in March to set up a joint "working group" to study sales of conventional arms. State Department officials said recently that the United States hopes to begin talks on on the question with the Russians by September.

The NSC study made public yesterday said "it will be most difficult to achieve the cooperation of the Communist suppliers," It noted that some of the largest purchasers of U.S. arms are motivated by Communist military support of nations on their borders.

While the United States is the largest arms supplier in overall dollar terms, the report said the Soviet Union is the leading worldwide supplier of supersonic combat aircraft, surface-to-air missiles, self-propelled guns, artillery and guided missile patrol boats.

The Defense Department reported that the Soviet Union has a substantial its production and saless of military items. The extent to which Russia would seek to move into the gap left by declining U.S. sales is "uncertain," the report said.