The United States still does not have the nine votes in the United Nations Security Council needed to impose economic sanctions against Iran, and it is uncertain whether the necessary backing can be won before 5 of the 15 council seats change hands on Jan. 1, reliable sources said yesterday.

According to the sources, the Carter administration, in its bid to increase U.N. pressure for Iran to free its American hostages, probably can count on seven votes from the current council membership for a resolution decreeing partial sanctions.

At present, the sources said, Washington can count on adding its own vote those of Britain, France, Norway, Portugal, Bolivia and, if the sanctions request is not too sweeping, Jamaica.

Kuwait, an Islamic neighbor of Iran that is fearful of stirring religious turmoil within its own borders, announced yesterday it will vote against a sanctions resolution, Bangladesh, another Islamic country in that region, also is expected to oppose sanctions, and the other council members reportedly are still on the fence.

As a result, the sources continued, the United States is intensifying its efforts to line up at least two more votes in hopes that a council meeting can be scheduled this week and a vote taken by Monday.

Routinely on Jan. 1, five of the council's 10 nonpermanent members will be replaced by other countries in the 152-nation world body. That would mean a further setback for the U.S. call, announced by President Carter last Friday, for quick action by the council to force Iran to comply with international law by releasing its hostages.

The turnover in council seats would force the United States to begin a new lobbying effort aimed at the incoming members. In addition, the sources said, U.S. officials believe that it might be even more difficult to get the requisite nine votes from the n ew lineup than from the council's current membership.

Also still unclear, the sources said, is the position of the Soviet Union.

As one of the five permanent members -- along with the United States, Britain, France and China -- the Soviet Union has the power to veto any action by the council; and despite heavy U.S. pressure for the Soviets to abstain, the sources said Moscow still has not revealed whether it will block the move for sanctions.

In response to questions yesterday about the maneuvering, State Department spokesman, Hodding Carter said only that Donald McHenry, U.S. ambassador to the United Nations, is continuing his consultations with other council members.

Carter also said he knew of no plans for Secretary of State Cyrus R. Vance to go to New York and join in the lobbying during the remainder of this week. Earlier, the secretary had been known to be tentatively planning to go there today. However, reliable sources said last night that, while Vance is keeping his schedule flexible and subject to change as circumstances dictate, it now seems unlikely that he will go to New York before Saturday at the earliest.

Ultimately, the sources added, the outcome of the sanctions move probably will be determined by how insistent the United States is about a strongly worded resolution calling for all U.N. members to comply with a trade boycott. According to the sources, there are still divisions among administration policymakers on this point.

Some senior administration officials, arguing that the most important thing is to demonstrate to Iran's revolutionary leaders that they are totally isolated in world opinion, reportedly want to press for a strong resolution that would exempt only Iranian sales of oil to other countries and Iranian imports of food and pharmaceuticals from a trade embargo.

But others in the administration, noting that Vance already has lined up the cooperation of America's major European allies for a trade and credit squeeze on Iran, contend that a loosely worded resolution would suffice, allowing most other countries to pick and choose what sanctions they would apply.

Those taking a soft line reportedly have argued, too, that a more generalized resolution would have a greater chance of warding off a Soviet veto and of winning the necessary additional votes from the undecided council members.

In dealing with the undecideds, the United States is understood to be trying very hard to woo China, which reportedly has promised not to veto a resolution but which also has not committed itself to a yes vote, and the three African members: Gabon, Nigeria and Zambia.

The membership changes on Jan. 1 will bring into the council only one country, the Philippines, that is considered a strong bet to support the United States. But, the sources said, that is likely to be offset by Gabon's replacement by Niger, which is regarded as more difficult to woo, and by the fact that the seat now held by Bolivia will be vacant for a time due to the Latin American bloc's inability to decide whether it should be taken by Cuba or Colombia.

In another development yesterday, Carter said the State Department is unable to account for the discrepancy between its contention that 50 Americans are being held in the U.S. embassy compound in Tehran and reports by three American clergymen that they saw only 43 captives there on Tuesday.

The situation was confused further by department officials who said they had been given a list of only 35 names of captives by the clergymen. However, one of the three, Rev. William Sloane Coffin, said last night in Tehran that he and his two colleagues have the names of all 43 persons they saw when they conducted Christmas services in the embassy.

Although Hodding Carter maintained that the number should be 50, he declined to make public the department's list of those it believes are in the embassy compound in Tehran.

Privately, department officials said the list was being kept secret primarily at the request of some hostages families. In addition, they added, the department does not want to make the list public because it might compormise the ability of diplomats and other third parties in Tehran to get into the embassy and report to Washington on conditions there.

In discussing the discrepancies, Carter noted that the clergymen saw the captives under difficult conditions and in different groups that may have made accurate counting impossible.