Washington — For the first time in half a dozen years, the United States now leads all other nations in arms sales to the third world. According to a recent Library of Congress study, the US has surpassed the Soviet Union in annual weapons deliveries to such countries. Those deliveries for 1983 totaled $9.7 billion for the US and $7.8 billion for the USSR. In arms-transfer agreements and contracts for future deliveries, the contrast is even sharper: $9.5 billion for the US and $4.2 billion for the communist superpower.
This indicates that the US lead in the government-sponsored international arms business is likely to hold for some time.
According to arms experts, this is the result of two things: the Reagan administration's view that weapons transfers are a legitimate major tool of foreign policy (a reversal of Carter administration doctrine); and the general recent drop in the world arms trade.
''We acquired a larger share of a smaller pie,'' says Richard Grimmett, national defense analyst with the Congressional Research Service.
This is causing growing concern on Capitol Hill.
''We firmly believe that the Congress has an overriding interest in reestablishing some meaningful form of control over what might otherwise be the unlimited and unrestrained sale of arms by any administration,'' four members of the House Foreign Affairs Committee wrote in a recent ''dear colleague'' letter. The four are Stephen J. Solarz (D) of New York, Benjamin A. Gilman (R) of New York, Michael D. Barnes (D) of Maryland, and Mark D. Siljander (R) of Michigan.
The US Supreme Court last year knocked out the legislative veto as a tool of lawmakers here. In an effort to circumvent this ruling, a bipartisan group of legislators is trying to amend the Arms Export Control Act to give Congress a role in limiting such weapons sales abroad.
The proposed amendment, which now has 35 cosponsors in the House, would require that Congress approve most arms transactions (government-to-government sales, commercial arms sales, leasing of defense items, and third-country transfers) involving at least $14 million in major weapons or $50 million in other defense equipment or services.
In emergencies involving US security, the President could act without congressional consent.
For certain countries - members of NATO, Japan, Australia, New Zealand, and Israel - the proposed congressional role would be less direct. Lawmakers would have 15 days to disapprove such sales or transfers, but would not have to act positively to approve them. The key political point here, as one congressional staff member puts it, is that the proposal ''treats Israel like a NATO ally.''
Even though Justice and State Department officials have said such enhanced congressional power over arms sales probably would survive a constitutional challenge, the proposed amendments are unlikely to become law soon.
Still, the pressure for more congressional say in the matter is likely to increase. There are a number of potentially controversial arms sales just over the horizon, especially if President Reagan is reelected. These may include renewed efforts to supply weapons to moderate Arab countries like Jordan, Saudi Arabia, and Kuwait, congressional observers predict.
When inflation is discounted, total arms deliveries to third-world countries are now less than they were in 1976, according to the Congressional Research Service report. There are several reasons for this, says Dr. Grimmett, the report's author.
World recession, mounting international debt, and a lessening demand for third-world oil have made it harder for many countries to keep buying more arms. Also, many arsenals are nearly full to capacity with advanced weapons acquired from communist and noncommunist suppliers.
''There was a tremendous amount of buying in the mid- to late-70s,'' Grimmett says. ''Certainly the drop-off is clear. Everybody's more cost-conscious now. They have to be.''
Even though Italy was the only major Western European supplier that did not show a drop in arms-sales agreements last year, noncommunist arms contracts in 1983 topped communist agreements by nearly 3 to 1. This puts into perspective the assertions by some conservative analysts that the Soviet Union and its allies are the chief culprits in conventional weapons proliferation.
Still, the Soviet Union from 1980 to 1983 led all other countries in the delivery of many major weapons, including tanks, artillery pieces, supersonic combat aircraft, and surface-to-air missiles. For example, the Soviet Union sent 990 tanks, self-propelled guns, and artillery pieces to Latin America during this period, compared to 466 from the US.
Grimmett warns against making too much of weapons numbers, however.
''As the history of recent conventional conflicts suggests, quality and/or sophistication of weapons can offset a quantitative disadvantage,'' he states in his report. ''Superior training, coupled with quality equipment, may, in the last analysis, be a more important factor in a nation's ability to engage successfully in conventional warfare than the size of its weapons inventory.''