Soviet diplomats are officially labeled friends of Laos and drive jeeps on country roads unescorted. Their American counterparts, normally confined to Vientiane, often wait days to arrange low-level appointments at the Foreign Ministry.

Perhaps 1,200 Soviet officials and dependents live in Laos. Staff plus spouses at the U.S. Embassy must not exceed 12, by orders of the Laotian government. One couple's Indian nursemaid has been counted against that quota.

Such are the constraints of life for the tiny American Embassy in Vientiane, the only place in Indochina where the U.S. flag flies and American diplomats drink to the health of revolutionary leaders at official receptions.

Once a huge U.S. mission directed B52 bombers and armies of hilltribe guerrillas against these same men. It distributed millions of dollars in economic aid.

The Americans who work just off Lane Xang Avenue in the chancery -- windowless as a wartime precaution -- are tolerated but hardly more by the pro-Vietnamese Pathet Lao, who swept aside a U.S.-supported government in 1975 with only a few shots fired.

The Americans chose not to leave. Charge d'affaires Leo Moser has the job of maintaining an American foothold while registering disapproal of Laos' alliance with Vietnam and the Soviet Union.

Aid is one point of difference. Washington is generally wary of giving anything that might be interpreted as war reparations or endorsement of the Pathet Lao. Moreover, U.S. legislation allows only humanitarian, not developmental, aid to Laos.

In the late 1970s, the United States did finance 11,000 tons of rice to cover food deficits caused by drought and flooding. It is also the source of some funds spent by U.N. development agencies. But Laos clearly feels that the destruction wrought by U.S. bombs warrants some direct aid.

Recently, a State Department doctor toured Vientiane's Mahasoth Hospital, built under the old aid program and now short of drugs, trained staff and parts for its equipment. "The Lao doctor who showed him around gave a lengthy plea for at least some American help," one Western diplomat recalled.

Any momentum toward a larger U.S. role in Laos has also been slowed by Laos' policies on some international issues sources said.Laos supported the Iranian militants' seizure of U.S. hostages and the Soviet invasion of Afghanistan.

U.S. claims that some embassy property was illegally expropriated in 1975 are another point of disagreement. Title documents to Silver City, a compound containing 17 small houses and some office buildings, are displayed periodically to the Laotians with little effect.

The embassy does not, however, contest loss of the large U.S. Agency for International Development compound, occupied by demonstrators and Pathet Lao troops in 1975. Fine print in AID agreements apparently allowed the government to end the projects at any time and size the AID offices.

Many of the Americans who worked in the antenna-bedecked compound were CIA officers and military technicians. The buildings are now the offices of Prime Minister Kaysone Phomvihan and other senior officials.

Despite deep differences, U.S. diplomats feel some quiet progress is being made. The two governments now cautiously exchange intelligence on narcotics trafficking. Laos also has helped help in the search for Americans listed as missing during the Indochina war and has returned some remains.

Consular duties could expand as Laotian refugees gain U.S. citizenship and exercise their right to seek entry for close relatives still here. It remains unclear how Vientiane would respond to such requests, however.

The mission also looks out after the six private Americans in Vientiane -- two couples administering small aid programs for the American Friends Service Committee and the Mennonite Central Committee, and two men who manage a private firm.

Government radio attacks the United States almost daily. But in Vientiane's streets Americans generally encounter smiles, not hostility. War rarely came to the city and many people remember the American era as prosperous times, in contrast to the lean years since 1975.

There is less affection for the East Europeans who have taken the Americans' place. A merchant's remark that "the Soviets are miserly" is typical.

Soviets are seen everywhere. Soviet women bargain for fruit and vegetables at early morning markets. This mystifies many Laotians; American women sent their servants.

Vientiane now bears a Soviet cultural imprint. Lenin portraits are standard furnishings in many offices. Bookstores sell Russian political works. Nighttime temple fairs which once showed sword-fighting movies made in Hong Kong now offer Soviet slapstick.

As the Americans before them, many East Europeans in Vientiane work in tight secrecy. My calls to four of their embassies, for instance, failed to elicit a single meeting.

Western diplomats believe many of the Soviets administer military aid. Technicians and pilot instructors probably have come with the Antonov transports, Mig jet fighters and helicopters of the Laotian Air Force that line the tarmac at Vientiane airport.

Others work in development projects. Soviet advisers help at a vehicle repair center and cement project north of Vientiane.East German technicians are said to be restoring telex facilities knocked out by lightning. t

Vietnam provides experts in irrigation and administration. But its more significant contribution is manpower -- soldiers numbering 40,000 by Western estimates who guard against guerilla attacks and build rural highways.

One Western aid official recalls visiting a southern province and seeing Vietnamese troops manning machine-gun nests along a road. Hanoi's soldiers also occupy camps ringing Vientiane and until recently patrolled the Mekong River banks to curb illegal crossings to Thailand.

Westerners report Vietnamese are seen only rarely in Vientiane government offices. There is little evidence that back-room advisers from Hanoi manage day-to-day decision making in the Laotian government, as often is the case with Vietnam's client government in Cambodia.

Laotian leaders have worked closely with the Vietnamese communists since the end of World War II. Having come to power with the backing of Vietnamese troops, they appear to see eye-to-eye on most matters with their opposite numbers in Hanoi.

As far as the Soviet Union is concerned, Laos does not have the strategic importance of Vietnam -- naval ports of call or airbases for reconnaissance aircraft. Moscow probably sees its aid to Laos as help to its prime ally in the region, Vietnam, and as harassment of China.