Iranians went to the polls today in a long-delayed second round of voting to elect members of parliament as Iran's revolutionary leader, Ayatollah Ruhollah Khomeini, urged the electorate to back "100 percent Islamic candidates."

After two days of hesitation, Khomeini also made public his approval of President Abol Hassan Bani-Sadr's plan for a provisional government. The plan is designed to bolster the president's faltering authority, which has come under increasing challenge from his right-wing clerical rivals.

Barring an upset, the clerical Islamic Republican Party, which captured most of the seats decided in the first round outright, is expected to control a majority in the 270-member parliament.

Despite Khomeini's pleas for a massive vote, the turnout appeared low -- perhaps the lowest in the five votes that have been held since the February 1979 revolution.

There were no reports of serious violence or vote rigging of the kind that marred the first round on March 14.

For Bani-Sadr, the naming of a government may serve to halt the Islamic Republican Party's steady erosion of his authority. His loss of power has been increasingly visible since the clerical party snapped back from the shock of his landslide presidential victory on Jan. 25.

Analysts today credited the president with a small tactical victory -- his first in months -- in that the Islamic Republican Party apparently dropped its opposition to naming a new government before parliament convenes in mid-June at the earliest.

Khomeini has said the parliament should settle the fate of the 53 Americans held hostage since Nov. 4. But without his direct intervention, analysts said the Islamic Republican Party again could frustrate Bani-Sadr's frequently repeated preference for a solution to the hostage crisis. It was the clerical party that prevented the Americans' transfer to government control early last month.

The clerical party is now said to be willing to accept a provisional Cabinet for the next two months, thus keeping alive its chances of naming a permanent prime minister on the basis of its expected parliamentary majority.

Still unsettled is the choice of a new prime minister to replace provisional prime minister Mehdi Bazargan and his Cabinet, which resigned in November in the wake of the seizure of the U.S. Embassy by militant Islamic students.

A front-runner for the prime minister's job is Adm. Ahmad Madani, a former Navy and defense minister who is favored by the middle class because of his record as a disciplinarian and his advocacy of law and order.

The parliamentary runoff election marks the completion of the cycle to install the revolutionary Islamic Republic's institutions, which began in March 1979 with a referendum that abolished the monarchy.

The vote today also constitutes the fulfillment of the 80-year-old Khomeini's dream, at a time when his health, to judge from his barely audible remarks on the radio this morning, appears to be far from good.

Fewer than 100 seats were won by the required absolute majority in the first round of parliamentary voting, in which more than 3,000 candidates competed for 270 seats, including 433 in the 30-seat Tehran constituency.

Results from the second round are promised within five days. But first-round results and the setting of a date for the runoff were delayed many times. The commission investigating vote-rigging charges from the first round has also yet to complete its reports.