Ayatollah Kazem Shariatmadari, the second most influential Shiite Moslem leader in Iran, today threw his support behind the appointment of Mehdi Bazargan as prime minister of an opposition provisional Islamic government. But he expressed veiled reservations about the autocratic way in which Bazargan was named.

This and more overt criticism from other quarters appeared to bring Iran's religious and political opposition closer to a potential rift over Ayatollah Ruhollah Khomeini's domination of the movement.

"We support Mr. Bazargan and hope he will be successful in his task," Shariatmadari said of Khomeini's appointment yesterday of the respected opposition figure. "We know Mr. Bazargan is a good man."

Asked whether he considered Khomeini's unilateral move legal, Shariatmadari said "If you ask whether it is legal according to Islamic law, yes it is. But if you ask according to international law, then you had better ask somewhere else."

Earlier Shariatmadari had expressed concern that an Islamic republic be established legally, have the support of the army and the people and be recognized by other governments.

In an interview at his house here, Shariatmadari was also asked whether all Iran's senior ayatollahs should participate in declaring an Islamic government, or whether Khomeini had the right to do it alone.

"A provisional government is formed only at critical times for certain reasons," he replied. "In these critical times when it is declared by one, if the others are not in agreement with him, they should keep quiet."

In Tehran, a lesser-ranking Moslem leader, Ayatollah Mahmoud Taleghani, was quoted by an Iranian newspaper today as saying he did not believe the appointment of a provisional government should be the monopoly of one man.

Last month Shariatmadari said he feared that if Khomeini pressed ahead too soon with his plans to install an Islamic government, it would risk an army reaction and "more violence and trouble." But his aides indicated today that at this "critical juncture," Shariatmadari would not voice any opposition to Khomeini's move, even though he might not be happy about it.

Shariatmadari also did not appear to go along with a statement Monday by Khomeini that opposition to his government would be considered blasphemy punishable by Islamic force.

Shariatmadari said he wanted to discuss this question with Khomeini later but that he thought dissidents who opposed the government should not be punished as long as their actions were peaceful.

In Tehran the English-language newspaper Tehran Journal openly criticized this aspect of Khomeini's statement.

Khomeini "has ordered the people to obey this new government or face being branded a traitor and dealt with accordingly under Islamic law," an editiorial said. "No one is even allowed to argue with the new provisional government."

"Apart from those that willingly support it, are we to see the others intimidated into support?" the commentary adds. "We have been promised that there would be freedom in the Islamic republic. But so far the evidence of freedom of choice has been remarkably lacking."