Sieu Luong Khanh had been planning his escape from Vietnam for four months and so the news that came over the Voice of America on July 21 and 22 was merely the clincher.

The broadcast told him that President Carter would order the U.S. 7th Fleet's help. They made it to Hong Kong in five days without serious incident.

Sieu Luong Khanh's tale of hearing Carter's commments is similar to that of many of his 4,000 friends in a dockside refugee transit camp here. They said in interviews today that although the presence of U.S. naval vessels and other nations' "mercy ships" gave them hope for escape, they would have tried to get out anyway.

In fact, they said, they had heard radio reports that the 7th Fleet was waiting to rescue them months before Carter's off-the-cuff comments and the formal pledges of stepped-up naval patrols were made at the Geneva conference last month.

None of them said the fleet's presence was vital to their plans but several said that a year of rescue stories, heard secretely on radios in Vietnam, had encouraged them to think that their chance of reaching safety were enhanced

Since the Geneva conference on July 20 and 21, the 7th Fleet has rescued several boatloads in danger of drowning and taken them to safety. But before the extra patrols were started, the Navy had rescues more than 1,200 drifting refugees and those rescues were reported by broadcasts into Vietnam. Italian rescue boats have picked up about 800 persons in recent days.

The rescues have become a controversial part of the international refugee politics because Vietnam has charged that they entice people to attempt escapes at sea.

Other countries are also unhappy. Hong Kong's chief secretary, Sir Jack Cater, said this week that the mercy ships may be doing more harm than good. Although he was referring specifically to private vessels, officials here said today he also has in mind the U.S. and Italian naval efforts.

Southeast Asian countries, which want the refugee exodus stopped inside Vietnam, fear the presence of rescue vessels will disrupt a tenuous truce and slowdown that came about as a result of the Vietnamese promise to try to curb the flow temporarily. Even Japan is concerned that the highly publicized rescue crusade would induce thousands to leave and complicate international resettlement efforts, according to officials in Tokyo.

The Vietnamese promise plus the rainy season and two large typhoons have resulted in a sharp decrease in the numbers of refugees washing up on neighboring shores.

The arrivals in Hong Kong, for example, dropped from more than 600 per day in May and June to only about 280 in July and most of those who landed here in July did so before the Vietnamese pledge was announced in Geneva.

Interviews in the dockside transit camp today also made it clear that the Vietnamese clampdown began nearly a month before the Geneva conference and included gunboat patrols and increased harbor guards designed to force fleeing refugees back to shore.

Toai Nguyen Quang, who had been a lieutenant colonel in the South Vietnamese Air Force, said the government's obstructions began in late June. Before that, he said, authorities did not care who left so long as they paid money to officials. But suddenly the government began stationing more patrols in harbors and began shooting at fleeing boats.

When he came out on July 18 as navigator on a boat that also carried his son and daughter, a Vietnamese gunboat tried to blast them out of the water, he said.

For three hours, the gunboat chased them, firing with what appeared to be a mounted antitank gun and automatic rifles. The government's boat was too slow and the refugees excaped after being hit only once by rifle fire.

Toai Nguyen Quang said he had heard radio reports for months on both the VOA and the British Broadcasting Corp. that U.S. naval vessels were picking up refugees. It was encouraging news, he said, but not the deciding factor in his flight.

As a former enemy airman, he had no job in Vietnam and was threatened with being sent to one of the government's "new economic zones." There he would be expected to farm dry, unproductive land and he feared he would die eventually of starvation. He knew he might die at sea in an escape attempt but he chose to flee anyway.

"All of us knew we risked the chance of dying," he said.

Another refugee, who said he had been a major in the South Vietnamese Army, sxcaped by walking away from a prisioner of war camp last month after being told by his wife by radio broadcasts mentioning that American ships were picking up boat people.

Toan Nguyen Thanh said his boat was at sea for 26 days and passed by 20 cargo ships, none of which would pick up him and his family although a few offered fresh water and blankets.

He said he would have attempted to escape without being aware of the U.S. Navy's presence. He shook his head when asked if he had been disappointed that no naval vessel came to his rescue.