Attracted by a chance to escape chronic poverty at home, growing numbers of young northern Vietnamese are seeking employment in the Soviet Bloc under an official labor export program, according to western diplomats here.

Their accounts of the program tend to contradict Reagan administration charges of possible human rights violations connected with it, including forced labor and harsh Siberian working conditions.

The diplomats confirm, however, that, despite Vietnamese denials, about a third of the Vietnamese workers' wages is deducted to help pay for imports from the Soviet Union and its Eastern European allies and another third is withheld for promised repayment to the workers when they return to Vietnam.

Even so, the diplomats say, the earnings are far higher than in Vietnam, and the workers are allowed to bring back consumer goods that either are unavailable at home or cost much more because of duties or black-market markups. In fact, the sources say, some Vietnamese even pay bribes of up to 10,000 dong (about $1,030 at the official rate and $95 on the black market) to secure jobs in Eastern Europe.

The program does have drawbacks for the workers, according to the diplomats, whose information comes from northern Vietnamese with relatives working abroad. But these are less serious than portrayed by Reagan administration officials, the sources say. Specifically they disagree with assertions that some Vietnamese are being forced to work in Siberia on a gas pipeline to Western Europe that has been strongly opposed by the Reagan administration.

"I'm convinced that no Vietnamese are working on the pipeline," one western diplomat here said. Another said that the Vietnamese were not working in Siberia but in the central and southern Soviet republics and that the worst weather they face is about 5 Fahrenheit.

The diplomats also assert that fewer Vietnamese are going to the Soviet Bloc than the estimates of up to 500,000 reported by the State Department.

Vietnamese officials refused to give details of the program, which they said falls under "labor cooperation" agreements between Vietnam and the Soviet Union and several Eastern European countries.

According to a State Department report to Congress last month on forced labor in the Soviet Union, Hanoi has sent Vietnamese citizens to work on several projects in the Soviet Bloc since 1981 under unpublished intergovernmental agreements that might violate international labor standards.

The State Department said reports have been received of "harsh--and, in some cases, involuntary--conditions" for Vietnamese workers, whose number it estimated at 100,000 to 500,000 for the 1981-85 period. The report quoted Communist news media as disclosing that about 45,000 Vietnamese workers are already on the job, about 11,000 of them in the Soviet Union.

"There is little doubt that the Vietnamese work for fixed periods--labor contracts are said to extend up to seven years--in a capacity similar to indentured status, with a substantial portion of their wages withheld to be credited against Hanoi's mounting deficits in these countries," the report said. It said Vietnam ran up a trade deficit with the Soviet Union of about $850 million at the official exchange rate--in 1981 alone.

Besides straight trade, western diplomats estimate Soviet Bloc aid to Vietnam at $600 million to $800 million a year, plus $400 million to $500 million in trade credits that are not repaid. The State Department report said that "at least one-third" of the Vietnamese workers' salary is credited to Hanoi's account in the country involved.

In addition to factory jobs, it said, Vietnamese are working on construction projects in southern Siberia. It cited a new railroad running parallel to the trans-Siberian line. The report noted charges that Vietnamese are working on the gas pipeline but said the allegations remained unsubstantiated. It also cited "potential for abuse."

According to diplomats here, however, many Vietnamese are eager to work in the European Communist countries. Most are young, single northerners, and many do not want to return to Vietnam, the sources said.

It is the Eastern Europeans that are less than satisfied with the arrangement, he said. "None is really happy with the Vietnamese as productive workers," he said, noting that Vietnamese "skill standards are very low."