President Carter said last night that Iran's conditions for the release of the American hostages "appear to offer a positive basis" for an acceptable settlement, but he refused to predict when the captive Americans might come home.

Carter, facing a difficult struggle for reelection in Tuesday's balloting, pledged that "my decisions on this crucial matter will not be affected by the calendar."

In a brief statement at the White House, following a day of meetings with his foreign policy advisers, Carter declared that any U.S. actions in response to Iran's newly stated conditions will be in keeping with "the honor and vital interest" as well as the laws and Constitution of the United States.

However, he shed no light on the U.S. actions or assurances that are being contemplated to meet the demands voted early yesterday by the Iranian Majlis, or parliament. It remained unclear last night, according to senior U.S. officials, exactly what U.S. actions would suffice to satisfy the Iranian conditions and thus bring about the release of the 52 Americans, who end one year in captivity today.

White House officials went out of their way to caution reporters against speculation that the hostages will be released today, the last day before the presidential election. Officials continued to declare that no advanced deal has been worked out to bring about the end of the hostages' long ordeal.

While it is possible that arrangements can be concluded quickly if Tehran authorities have the will to do so, the relatively detailed conditions adopted by the Majlis added a new level of complexity to the general principles of Iran's position announced last Sept. 12 by Ayatollah Ruhollah Khomeini.

As of last night, there was no clarification from Tehran of how strictly and literally Iran would interpret its announced conditions, and there was not even an authorized and official version of the conditions received through diplomatic channels.

One of the major U.S. problems was that it was not in direct contact with Iran to explore the terms of the announced conditions. Complicating the matter further was a report that Khomeini had ordered that there be no "negotiations" with the Americans, who would thus be left to accept or reject the conditions as announced and interpreted in Tehran.

"It all depends on what they mean by the conditions," said an official, who said that Carter would not be able to comply with several of them in the most strict interpretations. At the same time, he noted that much could be done in each of the specified areas within the guidelines previously laid down by the Carter administration, and thus an Iranian conclusion that the conditions were being satisified was not out of the question.

It was considered a significant and hopeful sign among senior officials that the Iranian demands made no mention of the areas that the United States had previously designated as out of bounds, including an apology from the United States for past actions in Iran and the removal of American airborne command and warning aircraft from Saudia Arabia.

One official said it was clearly evident that Iran had gone out of its way to limit its conditions to things the United States can deal with. This was believed to suggest a desire in Tehran to make an actual settlement, though on the stiffest possible terms that could be obtained from Washington, in keeping with the Iranian penchant for tough bargaining and the needs of Iranian politics.

Officials also said they considered it significant that there was no explicit mention in the Iranian statement of the spare parts and other military gear that Iran previously had bought, which remains in the United States under a presidential embargo. The arms are the most difficult and sensitive issue for the United States because of the war between Iran and Iraq.

It was unclear, however, whether Iran would consider the spare parts issue to be covered under the heading of "assets" that have been blocked by the United States.

Though Carter and some administration aides placed a hopeful interpretation on Iran's conditions, there was also a recognition in the administration that the legalistic and stiff decision of the Majlis might lead to a new impasse or even a new crisis in the often disappointed effort to free the Americans. One official, asked what he expected from the developments, replied: "Heartache."

Although the Majlis commission recommended that the hostages be turned over to Islamic courts for trial and punishment if the Iranian conditions were not met, senior policy-makers did not appear to take this threat at face value. The threat of trials for the hostages has been expressed from time to time in the past, but the Iranians have backed off in the face of strong U.S. warnings.

The suggestion from Iran that the hostages would be released in stages, as the United States implements various parts of a settlement previously agreed in principle, posed a problem for the United States. The Carter administration has consistently called for the release of all the Americans, and stated in past that the punitive actions against Iran cannot be rescinded for the return of less than all of the hostages.

There was no hint in the remarks of officials yesterday that the United States has modified its opposition to a partial, as opposed to a full, release.

The long-delayed actions of the Iranian parliament, which placed Carter under immense political pressure heading down the home stretch of his reelection drive, were conveyed to the president in the predawn hours in Chicago by Deputy Secretary of State Warren Christopher.

Carter broke off his planned campaigning for the day and hastily returned to Washington, where he met for two hours in the morning and an hour in the afternoon with his foreign policy advisers.

Appearing in the White House press room to report to the public at 6:22 p.m., Carter appeared extremely tired and drawn, his face puffy from fatigue.

The White House announced that Carter has canceled the initial appearance scheduled for today, his last day of election campaigning, apparently to meet his foreign policy advisers after receiving overnight reports from Tehran. And reporters were cautioned it is not certain that Carter will proceed with the rest of the marathon day he has scheduled -- campaign stops in Ohio, Illinois, Missouri, California, Oregon and Washington before flying in the early morning hours to his hometown of Plains, Ga., to cast his ballot Tuesday.

In his brief public statement, Carter appealed to national unity and said the administration was in contact with his main opponents for the presidency, Republican nominee Ronald Reagan and independent candidate John B. Anderson, as well as the congressional leadership of both parties. The White House made public a list of seven senators and eight members of the House, both Democrats and Republicans, who were being briefed by the State Department.

Saying that many months ago he had "made clear the steps that we would be prepared to take when the hostages are released," Carter suggested, without officially stating, that his actions now will be limited to those the United States was willing to take last February and March, in the earlier intensive phase of diplomacy.

Describing the new Iranian conditions as "a significant development," Carter went on to say with cautiously chosen words that "as we understand the parliament's proposals, they appear to offer a positive basis" for achieving the twin objectives of protecting American honor and vital interests, and working for the earliest possible safe release of the hostages.

Carter said that "we are pursuing the matter through diplomatic channels." Officials said the administration has been in touch in recent days with nearly all those who have served as intermediaries with Iran in the year of the hostages' captivity.

The most important channels of communication at this point, when the decisions in Iran have been officially placed in the hands of the executive branch of the Iranian government, are believed to be the offically designated channels -- the Swiss Embassy, which represents U.S. interests in the Iranian capital, and the Algerian Embassy, which represents Iran in Washington.

Former Iranian foreign minister Sadgh Ghotzbzadeh, appearing on "Issues and Answers" (ABC, WJLA) from Tehran, said that "physically it would be impossible" for the hostages to be returned by Election Day but expressed hope that "within one week, the whole thing will be over" if the United States accepts the Iranian terms.

Former secretary of state Henry A. Kissinger, appearing on the same program, called the hostage episode "humiliating" and accused the Iranian government of "attempting to influence the American election."