The Carter administration has taken up the challenge of paring down one of Washington's most entrenched bureaucracies, the 1,400-member secretariat of the Organization of American States.

Since the United States contributes two-thirds of the OAS budget, which now totals $81.3 million annually, it carries a lot of leverage. At the same time, however, the U.S. delegation is pursuing a separate goal announced earlier of reducing its budgetary contribution to 49 per cent.

The staff reduction supposedly is designed to increase OAS responsiveness to the needs of the 25 member nations, with more staff on field projects and fewer behind desks at the headquarters here. So the only overt opposition to the latest U.S. initiative is from thos whose jobs are threatened.

Indeed, Secretary General Alejandro Orfila has proclaimed the same objective of whittling down the bureaucracy. In 1976, a year after office, he admitted to utter frustration.

"I can fire anyone," he said at the time.

The member countries, especially those complaining that their annual dues are too high, rallied to defend the positions of their own nationals on the secretariat who were threatened by cutbacks.

U.S. officials say their budgetary pressures are meant to support Orfila's effort.

"We have to face problems that haven't been faced, to reinforce Orfila's attempt to do something about them," said Irving Tragen, newly appointed deputy to the head of the U.S. delegation, Ambassador Gale W. McGee.

It is a brusque form of support. The U.S. initiative came two weeks ago during a special OAS assembly to consider Orfila's proposed $89 million budget for 1978. A committee headed by Panamanian Ambassador Nander Pitty Velasquez had already cut $5 million.

"Only a rapid and energetic revitalization," said Pitty, "can undo the concept held by many that the OAS is a second-class organization."

The assembly trimmed another $4 million from Orfila's budget and still the U.S. delegation was unsatisfied.

"We think at least an additional $1 million could have been saved," Tragen told the assembly.

"Let me propose specifically that the secretary general submit his 1979 budget at the same level of assessments as for 1978," he added. The upcoming budget was approved 23-0, the United States abstained.

"Much of the reduction for 1978 is in the area of technical services to governments. In 1979, there should be no further cutbacks in these areas unless programs are completed or no longer desired by the member governments," Tragen said. He called for elimination of 90 more jobs in 1980 in addition to the 68 to be dropped in 1978.

Orfila said he had no quibble with this, noting that he has already cut the staff to 1,463 from 1,579 when he took over.

"We have maintained and sometimes increased programs" ranging from technical assistance to scholarship grants, he said. Still, he expressed concern that the larger countries are showing a reluctance to increase their contributions even as administrative costs come down.

Staff members complain that the cutbacks in fact do cut performance.

"We used to maintain parity with salaries at the United Nations," said one technician. "For two years we've been falling behind. High quality people are not going to stay."

With this in mind, the OAS is undertaking studies so that by the foreign ministers assembly in June, policies on wage raises and elimination of jobs can be adopted without what Tragen called "a meat axe approval."

At that same June meeting, Ambassador McGee has made clear, the United States expects action to reduce its budget share to 40 per cent. In the OAS, as in the United Nations, the Carter administration wants to avoid the appearance of the domineering role that comes with being the major source of funds. For the OAS, that means that 1979 budget, already under structure not to expand even to accommodate inflation, will have to shrink further unless Latin countries are willing to increase their quotas.

One proposal is to fix a minimum contribution that would raise the dues of proliferating small states. Grenada's current quota is $13,311, Barbados' $35,496, and 14 other nations pay less than $80,000 each.

The two largest contributors after the United States are Brazil and Argentina, which have a different perspectiveon the budgetary crunch. Again in accord with U.S. initiatives, the one OAS dependency to see its share of the budget trebled was the Human Rights Commission.

With funds for on-scene investigations greatly expanded, two likely targets of the commission are Brazil and Argentina.