The downing of a transport plane over Nicaragua Monday raises new questions about US support for the anti-Sandinista contra guerrillas. A government spokesman in Managua said Eugene Hafenfuf, the survivor of the downed aircraft, which was filled with arms apparently destined for the US-backed Nicaraguan resistance, identified himself as a US military advisor based in El Salvador.
Secretary of State George Shultz, responding at a news conference yesterday, conceded the plane was chartered by Americans. But he insisted that ``they had no connection with the US government at all.''
Several private analysts say the crew of the downed aircraft, while probably having no official US connection, may nevertheless have been acting at the direction -- or at least with the foreknowledge -- of the Central Intelligence Agency (CIA).
US officials say the government has remained at arm's length from private groups that have supported the contras during the period when US funding was cut off.
But retired US Army General John Singlaub, who has spearheaded private efforts to channel arms and supplies to the contras, said Sunday on the CBS program ``60 Minutes'' that CIA director William Casey has ``indicated approval, and he has been encouraging.''
At least two Americans, members of paramilitary organizations backing the five-year contra war, have been killed inside Nicaragua in recent years.
Last August Congress approved $100 million in mostly military aid to the contras. The legislation provides for US training and arms shipments to the 20,000-man contra force. But those activities are barred until the contra aid package clears a final legislative hurdle, expected before Congress adjourns.
Under existing ground rules that accompanied the passage of $27 million in humanitarian aid to the contras last year, the CIA is denied any direct or indirect operational role in supplying or training contra forces.
A spokesman for the CIA, Sharon Foster, said yesterday there was no CIA connection with the aircraft and said the pilot ``is not associated in any way with the agency.''
``Congressional restrictions prohibit the agency from supporting the contras and we have not violated the law,'' Foster said.
But some critics of the Reagan administration's Central America policy say they're not convinced.
``The Reagan administration has a long record of ignoring the Congress on Nicaragua,'' says Laurence Birns, director of the Council on Hemispheric Affairs. ``The leitmotif of US policy has been with or without permission we won't abandon support for the contras.''
Critics point out that the US has long been eager to create a viable southern front, based in Costa Rica, to complement the main contra strength now concentrated on the Honduran border. They speculate that the aircraft shot down over Nicaragua may well have been contracted at the behest of US officials, or at least with their knowledge, for the purpose of delivering supplies and trainers to a covert Costa Rican base camp or directly to contra forces operating inside Nicaragua.
``There's no question that the US is involved in strengthening the second front since that's been a long-term strategic desire within the Pentagon,'' says another Washington-based Nicaragua expert.
Intelligence gathering missions over Nicaragua are legal. But military experts point out that it's unlikely the US would use such old and slow-moving aircraft for such purposes.
Nicaraguan authorities say the C-123 was shot down by Sandinista forces using Soviet-supplied, portable anti-aircraft rockets. They said the plane was crewed by four American military personnel including Hafenfuf, the one survivor.
The Nicaraguans have so far produced no evidence of their claims, noting that bad weather has so far prevented military officers from escorting newsmen to the crash site.
Spokesmen for the Sandinista government say the aircraft was loaded with 50,000 rounds of ammunition plus Soviet-made assault rifles and grenades. One source familiar with CIA operations says it is a common practice for the agency to supply Soviet-made weapons purchased on the international arms market to allow plausible deniability in just such cases.
Congressional sources say even if Nicaragua was to prove Hafenfuf was a US military advisor, it's unlikely that Congress would reverse itself on contra aid in an election year.
``It's not likely that anything, including this, will throw contra aid off track now,'' says one congressional aide.
But if administration denials are proved false, Congress could eventually act to tighten the restrictions that accompany new US aid to the contra forces. US military personnel would be barred from operating within 20 miles of the Nicaraguan border, though non-American advisors working under contract could accompany the contras inside Nicaragua.