Some 800 Moslems who journeyed to the Islamic Center Tuesday to celebrate the end of Ramadan were suprised to find out they were a day late.

Although the holiday, Id al-Fitr, was scheduled for Tuesday, the lunar month of Ramadan actually ended Sunday night, when Middle Eastern Moslems spotted the new moon, accordingto Muzammil Siddiqi, the new deputy director and imam, or spiritual leader, of the Islamic Center on Massachusetts Avenue NW.

As a result, the Id prayers that endthe month of daylight fasting for faithful Moslems, were hastily rescheduled here and in New York for Monday. fOnly 2,000 to 3,000 Moslems turned outfor out services here Monday, according to Siddiqi, compared with 5,000 people last year.

The holiday mix-up was the second disappointment this week for many of the 50,000 Moslems in this area.

On Monday, a Moslem group canceled "Islamic Festival U.S.A. 1980," a day long festival of prayers and cultural activities scheduled to take place Tuesday on the Mall.

Miraj Saddiqi, president of the Muslim Development Corporation, who is not related to the imam, called off the public celebration, fearing interference from Americans who wouldn't "distinguish the Moslem worshipers from the Iranian students." A number of Americans had hurled verbal assaults and tomatoes and eggs at protesting Iranians last week.

In accordance with Islamic custom, those attending Tuesday's service went through the standard Id prayer and ritual, made contributions and listened to a sermon.

But unlike previous celebrations, Monday's sermon by Iman Siddiqi and Tuesday's sermon by a local Moslem, Zakiudim Shaidh, touched on social and political issues, including the Moslem refugees of Palestine, Eritrea and Somalia, and the recent naming of Jerusalem as the capital of Israel.

Following the sermon, an unidentifiedAmerican black Muslim read a letter from Hammaas Abdul Khaalis, who led 12 Hanafi Muslims in the March 1977 takeover of three Washington buildings, including the Islamic Center. Khaalis was convicted of murder and is serving a 41-year sentence at the Federal Metropolitan Correctional Center in Chicago.

"Palestine is the national home of all Palestinians and all who wish to live in peace with them," the letter stated. "No one can deny that Ayatollah (Ruhollah) Khomeini of Persia is speaking the truth in regards to the enemies of Islam," the letter said.

"Al-Aqsa Mosque in Jerusalem must not be in the care of the hands of the enemies of Islam," the letter continued. "Innovations have brought about disunity in (the laws of) Islam, but remember Allah curses the innovator and Allah also curses the one who showsrespect to the innovator."

Siddiqi said he knew nothing of the letter, and because of the confusion and noise caused when many of the worshipers left after the sermon, he said he didn't realize it had been read until questioned by a reporter.

Such political statements would have been prohibited under the administration of Mohammad Abdul-Rauf, who was the center's imam until last Friday. Rauf will step down as director in December.

But Siddiqi, 38, a Harvard PhD who most recently was chairman of the religious affairs department of the Moslem World League in New York City, said he welcomes political discussions at the center "after prayers."

"In Islam there is no division between religion and politics," said Siddiqi. "We have to see everything from the Islamic point of view whether social, economical or political."

Siddiqi said, "We have no disagreement with the Iranian revolution . . . The shah was oppressing the people." In a reference to Khomeini, he added, "I do not support anybody 100 percent, only the prophet Mohammed."