The captains and the kings of Idi Amin's Uganda streamed into Kenya today leaving their once fearsome master virtually alone to contemplate the final lapse of his eight years of rule by terror.

At this same border crossing where Amin's henchmen had forced the cream of Uganda's establishment and society to flee for its life, the tables were turned.

From the newcomers came a tale of decline and fall, disintegration capped by rumors of yet more massacres-this time between Christians and Moslems-to cap the thousands of Ugandans who have perished violently under the one-time Army boxing champion.

What emerged from often incoherent statements was an absence of even what passed for constituted authority in the heyday of Amin's rule.

By rank and protocol the most important refugees were the governors and district commissioners of the capital of Kampala and of Jinja, the town on Lake Victoria wher Amin once swore he would stage his last stand against the now triumphant Tanzanians and Ugandan exiles.

But the most significant were the dozens of captains, majors, lieutenant colonesl who left their troops in the lurch and slunk across the border.

The final proof that Amin was abandoned by all but the diehards was provided by the defection of the commander of the Jinja-based Muammar Qaddafi Battalion named after the Liebyan leader who sent rroops in an ill-fated effort to stave off the inevitable defeate.

Kenyan residents reported that the commander surrendered at noon at the border crossing at Malaba, 20 miles north, and was granted asylum.

Just to make sure that the stragglers from Amin's army lay down their weapons and cause no troubles as the price for receiving asylum, Kenya overnight dispatched to the border area 3,000 troops in 300 trucks and armoured vehicle.

Idi Amin, the self-styled field marshal, president for life and conqueror of the British Empire, was said to be somewhere between Jinja and Tororo, a town near the Kenyan border farther north.

"Amin's said to be hiding out in the forest with his bodyguards to protect him against Ugandan exiles' kidnap squads dressed in civvies that have been sent to capture him and bring him back alive," a Kenyan official said.

The most forlorn refugees-Kenyans estimated them at 80 percent of the hundreds who came across today-were Nubians, a tribe from northern Uganda and southern Sudan.

They cashed in handsomely under Amin and along with his own Kakwa tribe and refugees from neighboring Rwanda were cordially detested and feared for their primordial rule in commerce and three branches of the murderous secret police.

Their dejected womenfolk stared endlessly into the distance, the men, some in Western suits, others sporting reflectingsunglasses, were a tight-lipped lot. At least they were safe.

The well off-those in the Alfa Romeos, the Peugeots, the Mercedes piled high with television sets, tape decks and record players-waited confidently and were finally driven off in a 21-car convoy with Kenyan police Land Rovers fore and aft.

The poor waited anxiously for the Kenyan customs and immigration officials to process their belongings-chairs, bedding, tables, foam rubber mattresses and suitcases piled high on hand barrows.

A teen-age son of an Eguptian businessman reported "no one is in control" in Jinja although the city was calm. He had seen "very few soldiers" on the 74 miles between Jinja and Busia.

"They're all fleeing for their lives," he said, "except three shabby soldiers we saw in Busia. They tried to stop us but we kept on driving."

Various refugees told various stories about massacres in the lawless sector east of Jinja near the Kenyan border, but it was impossible to tell whether Amin's men, mostly Moslems, were massacring Christians or whether the Christian majority was taking vengence on the tiny Moslem minority, as seemed more probable.

A Kenyan said, "Amin's people, the Moslems, are not loved. It's just the beginning, the beginning of the revenge killing."

A somewhat tipsy Ugandan immigration official warned, "Don't write stupid things. But if you are a tourist and want a visa, I'll give you one." He smiled hideously, perhaps understandable in his present circumstances.

Only yards away stood a young Swedish diplomat. He had been dispatched here in so far unavailing effort to discover if indeed, as rumor has it, two Swedish and two West German newsman are still alive despite the almost certain knowledge they were executed a week ago by Amin's goons.

Amin had not issued visas to journalists for more than a year and the four Europeans were caught as they tried to slip into Uganda in a boat on Lake Victoria to chronicle his final days.

Still waiting for clearance were three Mercedes buses jammed with Nubian women and men. On the buses' sides was inscribed in red letters "Freedom Tours and Travel."

A Kenyan immigration man saw a visitor looking, nodded, then laughed: "Yes, it's a bit confused. One set of Ugandans is ending its exile while another is just starting theirs." CAPTION: Picture, A Kampala street is littered with glass and debris after widespread looting throughout the Ugandan capital.AP