As evening falls, people huddle under plastic bags to sleep on the sidewalks. By day, curbs are lined with peddlers, often school-age children selling black-market British or American cigarettes at $7 a pack. Everyone seems to be working the ration-card racket, trading off or selling one card or another to try to buy precious soap, fruit or rice.

It would be a normal street scene for the capital city of almost any other developing country. But for the proud, almost prudish Vietnamese, such scenes are a reproach to their vision of the society they have fought to build through three decades of sustained warfare.

Officials shut their eyes to the visible evidence. They say there is no unemployment in Hanoi, that everyone receives a monthly ration of 26 pounds of rice and has a right to public housing. They say Hanoi does not have a black market, only an "open market" where prices are three to seven times the government-set rates.

For black markets, corruption, profiteering or idle workers, one is directed to go south, to Ho Chi Minh City, the former Saigon.

There is still a different vitality in that southern city. Yet with the outlawing of drugs and prostitution, the closing of most bars and clubs and the imposition of a communist system over much of the economy, Ho Chi Minh City is hardly a center of Western decadence. In Vietnam's official view of itself, however, Hanoi remains the honorable capital of victorious Vietnam, while the former Saigon is the unworthy seat of the old enemy. Ho Chi Minh City has become the scapegoat for many of the nation's problems, and the leadership's wartime vision of the world need not be disturbed.

A first trip through Vietnam since the war's end is a constant play of illusion on reality: the official version against the actual Vietnam. But through the journey, themes emerged reflecting the difficulties facing Vietnam's faltering revolution:

The experienced, unified party leadership has become calcified, unable even to acknowledge Vietnam's problems, much less find creative solutions. This is particularly evident in the mishandling of the integration of the south.

The country has failed to put aside its habits of war and build a peacetime nation. Instead, it is returning to militarism.

The exuberance of the 1975 victory over the U.S.-backed government in South Vietnam has waned. Official newspapers now warn against pessimism. The people are living in worse poverty today than during the last years of war.

The Vietnamese are no longer the victims of Japanese, French or American armies. They have themselves become a foreign occupation force in Cambodia. There is evidence now that the Army is behaving like any other such force, plundering a famine-threatened nation.

While no bloodbath followed the 1975 victory in the south -- as U.S. officials predicted -- experts in Ho Chi Minh City estimate that over half of the southerners want to leave the country.

The Vietnamese know they are in serious trouble, but they continue to look abroad for the source of all their problems. They see China and the United States unleashing and manipulating the forces that continue to divide Vietnam. They do not see the sign that their revolution itself appears to have petrified in Hanoi under the pressures of war and that they have extended into the south not a fresh revolution but bureaucratic and military control.

"No one has a greater respect for what the Vietnamese did than I," said a representative from a Third World country. "The news of Dien Bien Phu in 1954 was inspiring for all of us. But what the diplomats call 'cassette number one' -- the phrase that 'we have fought 30 years of war, we are very poor' -- has become tired. They defeated the Americans.They should be proud and get on with it."

"They cannot break their habits of war," said a Western official in Hanoi."They try their old remedies on new problems and if it doesn't work, they won't change."

Contacts with foreigners during my 17-day trip through unified Vietnam were relatively easy and many of them felt free to speak frankly. The Vietnamese government arranged most of the rest of my schedule as is their custom, including lectures on American war crimes and visits to battlegrounds on the border with China to underline their claims of Chinese aggression.

Officials and outsiders all agree that confronting the external danger has replaced integrating the south in Hanoi's national priorities. But some knowledgeable and sympathetic observers of Vietnam's long struggle are now beginning to wonder if the aging leadership is turning to fear of foreign domination and a renewed emphasis on militarism as a substitute for the new and fresh approaches they have not found in peacetime.

After the death of Ho Chi Minh in 1969, there were virtually no signs of a leadership struggle or moves toward internal change. The major outcome, foreign experts in Hanoi now agree, was the loss of the revolutionary leader's moderating voice toward China and a resulting move away from Peking.

Headed by President Ton Duc Thang, 90, and Prime Minister Pham Van Dong, 73, the government is something of a gerontocracy. The average age of the members of the national assembly is 72 years. The party, headed by veteran Secretary General Le Duan, 71, has an average age for its members of 40 years, a point recently severely criticized by the party newspaper.

"They wouldn't like to admit it, but I think this shows the Confucian streak in them, their respect for old age." said one well-informed diplomat. "Nothing bothers them more about China than the ease in which national leaders are purged and disgraced."

One of the men said to have prospered from the anti-Chinese sentiment in the party is Gen. Vo Nguyen Giap, who at the age of 67 is reportedly considered by his peers to be youthful and the likely successor to Pham Van Dong. Earlier this year, Giap delivered the "state of the state" address rather than Dong, a sign to many that Giap already has usurped some of Dong's power and, alone with Le Duan, is running the country.

Giap, the hero of Dien Bien Phu, appears to be the man molding Vietnam's return to militarization to ensure its control of Cambodia and bolster its defenses against China. War and the Army again are meant to pull the country together.

"Everything changed with the Chinese invasion," said a well-informed diplomat who has lived for some years in Vietnam. "Hanoi played the occupation of Cambodia here as a popular uprising so it meant far less to the people than the Chinese invasion. Defense of the fatherland is excuse enough for the problems they're facing."

Ironically, the tangled web of relationships between Hanoi and Washington has again become central to Vietnam's efforts to stave off a new invasion by China, to rebuild the south and perhaps indirectly to point Vietnam toward a new generation of leadership.

Nguyen Co Thach, 59, is the acting foreign minister. He is, in fact, charged with normalizing relations between his country and the United States and he is proceeding with stubborn determination despite Washington's clear reluctance.

Hanoi's leaders, who were so skillful at putting across their position in the American political debate during the war, have failed to do so in peace. They miscalculated by insisting on U.S. aid too long and then dropping their demands just as the United States was cementing its strategic friendship with China and turning away from Hanoi. Thach is credited with finally shifting the Vietnamese negotiating position and he is the man who now hosts visiting American journalists and politicians. This, and his mental agility, make him known around Hanoi as "the double-headed fox" and "Mr. America".

These nicknames also reflect the dilemma Thach must resolve. The Vietnamese are turning to the United States, their old enemy, to establish a presence in Vietnam and bring political and economic relief to the suffocating landscape of Soviet dependency as well as restrain the Chinese. Finally, any discussion of U.S.-Vietnamese relations returns to China.

During an interview at his office, Thach described what he considered the damning event which told Vietnam how dangerous the Chinese had become. When the Vietnamese perceived that Mao, the party chairman, was capable of killing China's president Liu Shiao-chi, during the Cultural Revolution of the 1060s, "we knew we must be prepared ourselves."

"During these 30 years our party has been united, not as in China, because we unite against all outside threats. Our biggest difficulty is with China. We feel the United States is playing the China card against Vietnam, and we hope the United States will stop it."