The United States continued to press today for U.N. resolutions on Iran and Afghanistan, but action on both issues was delayed by procedural problems and reservations on the part of other Western and Third World backers.

An expected Security Council vote to present the Afghan issue to the General Assembly was postponed. Yesterday, the Soviet Union vetoed a resolution in the council calling for withdrawal of its troops from Afghanistan.

Third World sponsors of the proposal to shift to the veto-free General Assembly spent the day privately debating which of them would be singled out for what they saw as the undesirable task of publicly calling for a special assembly session.

No movement was reported on a U.S. draft resolution calling for economic sanctions against Iran. Although the Jan. 7 deadline set last week for the release of American hostages in Tehran has passed, U.S. diplomats now say the sanctions resolution will not be presented to the Security Council until at least Thursday. Its eventual passage is in question.

While U.S. diplomats repeatedly have emphasized that the two issues are unrelated, the fact that they have overlapped here has presented many U.S. delegations with difficult internal and international political problems.

The U.S. draft resolution on Iran, calling for embargo of all exports to that country except food and medicine, is now being negotiated with America's Western allies. Some of them have objected to wording that would cancel previously existing contracts and lines of credit.

Based on earlier consultations with the Europeans, U.S. diplomats say that the differences do not affect the substance of the resolution and that their Security Council votes are assured.

The question of which of the Third World council members -- including Jamaica, the Philippines, Mexico, Zambia, Bangladesh, Tunisia and Niger -- will vote for the sanctions resolution is a more complicated one that in part has become tied to the Afghan situation.

Based on the advice of sympathetic Third World governments and some of its own policymakers, the United States has let the Third World, and primarily non-council member Pakistan, take the lead on the Afghan resolution. But as harsh rhetoric on the subject between Moscow and Washington had increased, it inevitably has turned the issue into a big-power debate as well.

Many Third World delegations, the majority of which belong to the 95-member nonaligned movement, are opposed to the Soviet invasion. Yet their own national policies require them to maintain their distance, at least in international forums such as the United Nations, from Washington.

A vote in favor of turning the Afghan question over to the General Assembly is increasingly seen here as a pro-U.S. vote. "The debate is now proceeding in the form of the Soviet Union being backed into a corner," one nonaligned diplomat said, "and many don't want to join it and look like they're siding with the West against the Soviet Union."

The perception becomes important, this diplomat and two others said, in terms of the subsequent vote -- again with the United States -- against Iran.

While the Third World delegations are acutely aware of the domestic pressure on President Carter to take aggressive action in the Iran crisis, a Third World diplomat said today, they felt that a U.S. push for a sanctions vote now would be "sheer stupidity."

One possible indication Washington may agree was today's administration assertion that no one is in charge in Iran. Economic sanctions may have little effect on the militants holding the U.S. Embassy in Tehran, Carter told congressional leaders tonight, since they are believed to be beyond the control even of that nation's Islamic leader Ayatollah Ruhollah Khomeini.

While U.S. officials insisted the administration will go ahead with the sanctions resolution, one informed administration source acknowledged that Carter's emphasis on the lack of effectiveness of sanctions was significant. It may prove the only way, he suggested, to defuse domestic pressure should the White House decide that sanctions could not be supported by a council majority and move to delay or withdraw the resolution.

To complicate matters still further, although two weeks ago it was assumed the Soviets would abstain from a resolution to punish Iran, U.S. diplomats now believe that worsening U.S.-Soviet relations have virtually assured another Soviet veto. Should that happen, the Security Council could find itself in identical situations on both issues -- deciding whether to call for an emergency General Assembly session.

Although such a call on afghanistan seemed imminent yesterday after the Soviet veto, Pakistan and the other sponsors of the original council resolution calling for the withdrawal of Soviet troops were unsuccessful in finding a Security Council member to request a vote on the issue.

Pakistan is not a member of the council. Yesterday, it was thought that the Philippines would take on the task. Earlier today, the Philippines foreign minister reportedly announced in Manila that his country would do so. But Philippine diplomats here reportedly never received such instructions.

Diplomats are hopeful of a solution by Wednesday. But if it does not come, a number of delegations were considering another route to the General Assembly.

Under U.N. procedures, any assembly member can ask Secretary General Kurt Waldheim to "poll" the membership of the body, probably by telegram, on holding a meeting. If a simple majority agrees, a session must be called within 24 hours.