Ayatollah Ruhollah Khomeini tonight brushed aside President Carter's warning against putting the remaining hostages at the U.S. Embassy on trail and said their "spying has been proven by evidence."

In a television address to the nation on the eve of what promises to be the largest demonstration yet outside the U.S. Embassy, seized by Iranian militants 17 days ago, the 79-year-old religious leader did not provide details of the alleged evidence.

His language, moreover, suggested that he had not yet clearly decided on the trials, which he first broached Sunday after announcing his decision to release 13 American women and blacks deemed "innocent of spying." The hostages were allowed to leave Iran early today and flew to West Germany where they joined three freed on Monday.

At one point tonight, Khomeini said, "Carter's disgrace will be when the spies are tried."

But in reiterating the Iranian claim that the hostages were not diplomats but spies, he used the conditional tense in talking about a trail.

If President Carter does not extradite the deposed Shah Mohammad Reza Pahlavi, he said, "It is possible they may be put on trial and Carter will know the consequences if they are . . .

"Carter tries to frighten us, sometimes militarily, sometimes economically," Khomeini said. "He knows too well himself that he is beating an empty drum. He neither has the military capability nor the following."

He contemptuously said, "All of Carter's actions on the hostages are merely part of his presidential campaign."

Khomeini's broadcast followed earlier suggestions that Iran was studiously avoiding pushing ahead with the spy trial and would welcome a lull in the crisis with the United States that is now in its third week.

Symptomatic of the feelings that time was on Iran's side were remarks by the director of Iranian radio and television, Sadegh Ghotbzadeh.

He said he doubted that the ruling Revolutionary Council "would even discuss" the question before the new Iranian week beginning Saturday. "We have more pressing problems."

Thousands of seemingly good-natured Iranians started coverging on the embassy this evening, keeping up a barrage of anti-American chants and slogans.

Ordered by Khomeini's office in the holy city of Qom, 80 miles due south of here, the parade coincides with the start of the month of Moharram, a period of mourning in Shiite Islam for its seventh-century martyr Imam Hossein, and his family.

Special attention is focused on this year's Moharram. It marks the start of Islam's 15th century, a convenient rallying point for the current anti-American campaign and the first annivesary of last year's mammoth marches that underscored the depth of anti-shah sentiment toward the end of his 37-year reign.

Tasua and Ashura, the two holiest days of Moharram, commemorate the defeat and subsequent death of Imam Hossein, second son of Imam Ali and son-in-law of the prophet Mohammed. This year the holidays fall on Nov. 29 and 30.

Observers here said the current anti-American campaign was likely to continue to grow until then.

Tonight, at the request of Khomeini, Iranians reenacted their defiant performance of just a year ago, when, braving the military government's curfew, they chanted "Allahu Akbar," or "God is Great," from the rooftops.

The demonstration Wednesday is being billed as a rerun of a series of marches last December in which millions of Iranians of all walks of life backed Khomeini's demand that the shah leave the country. Now they are backing the ayatollah's insistence that the ex-ruler be returned for trial and, presumably, execution.

Schoolchildren have been given the day off, evidently to participate in the demonstration.

In their 41st communique since seizing the embassy Nov. 4, the radical Islamic students holding the hostages said: "Last year in Moharram the Iranian nation, with the cry of 'God is Great,' frightened the powerful shah so much that in a short time he was overthrown.

"This year, which is the beginning of Moharram, the fall of the devilish power of the United States," the communique added, "will be the good news."

Describing the current crisis as a "crusade of God's servants against the great Satan of the times -- the United States world predators," the communique said, Khomeini "still attacks the heart of the idol temple of the White House like Abraham with an axe in his hand."

Meanwhile, diplomats reported no progress in efforts to persuade Iran's acting Foreign Minister, Abol HassanBani-Sadr, to allow a foreign ambassador to visit the remaining 50 or so hostages at the embassy each day.

The idea was first broached last week because of the diplomatic community's "growing concern about the conditions ofdetention there."

The hostages released earlier this week have confirmed reports that they and their colleagues were bound all during the day and sometimes even at night.

Also worrying diplomats was the inability of previous diplomatic visitors to see some of the hostages, raising fears about their well-being. The diplomats now have asked to see every single hostage.

In another development, the official Pars News Agency added further confusion to the off-and-on Iranian decision to refuse dollars in payment for oil sales.

"From now on," a Central Bank official was quoted by Pars as saying, "we accept only French francs, German marks and Swiss francs." Later the agency retracted the report without explanation.