Ayatollah Ruhollah Khomeini assured Iranians by radio from his hospital bed in Tehran yesterday that his health is "not bad" and urged them to vote in today's presidential election.

Khomeini was taken to the hospital in Tehran Wednesday from his home in the holy city of Qom for treatment of an unspecified heart ailment. Today, however, the 79-year-old leader of Iran's revolution said his illness "is not important," according to a Reuter report on the 10-minute broadcast, which was repeated several times yesterday on Iran's state radio.

The reports of Khomeini's illness heightened tensions in an atmosphere already strained by the election, which is the first real expression of public will since February's clergy-led revolution toppled Shah Mohammad Reza Pahlavi.

Since the revoluton, the electorate of 22 million has voted on establishment of an Islamic republic and approval of a new constitution, but it has yet to be called upon to voice a preference for a national leadership.

The list of front-runners in today's election offers a real choice: Finance Minister Abol Hassan Bani-Sadr, a proponent of nationalization and radical Islaic economics; Ahmad Madani, the former naval commander and advocate of strong central government, who has the support of Iran's middle class, and Hassan Habibi, spokesman for the governing Revolutionary Council, who has the backing of the clergy.

All three main contenders -- 66 candidates remain in the race -- are believed to prefer an early end to the American hostage crisis, and diplomatic observers believe the presidential election could give them the mandate to speed up negotiations.

The election also will test the strength of Iran's troublesome regional autonomy movements. If the Azerbaijanis in the northwest and the Kurds in the west boycott the contest, their relationship with the central government will be strained further.

The president, although second in power to Khomeini, will be able to nominate the prime minister, sign treaties and international agreements and send proposed legislation back to the Cabinet.

The Iran's current political chaos, however, his powers will likely be enhanced since, aside from Khomeini, he will be the only person with a popular mandate. Should Khomeini's illness incapacitate him, the role of the president would become even more important.

In the diplomatic maneuvering over the fate of the hostages, and that of the deposed shah, Foreign Minister Sadegh Ghotbzadeh backed away somewhat from his claim of Wednesday that the shah had been placed under arrest in Panama, where he is currently living.

Yesterday, Ghotzbadeh -- who is also a candidate for president -- said the shah was "sort of" under arrest, although Panamanian officials said the shah is free to travel "wherever he wants to, within Panama or abroad."

The Panamanians say that a telegram sent to Iran saying the shah was "under the care" of Panamanian authorities was not meant to imply his being under arrest or detention. A U.S. official cautioned in Washington that Panama's somewhat vague lanuage and the Iranian response could present problems.

"We are not hopeful one whit that this is going to lead to the release of the hostages," the official said. "Governments without the three months' experience we have with the Iranians want to explore it. The danger is that this could lead to false impressions."

The militants who have held the Americans hostage at the U.S. Embassy since Nov. 4 dismissed the contacts between Ghotbzadeh and the Panamanians, whom he has asked to extradite the shah, out of hand, according to Reuter. The news agency quoted one of the militants as saying, "... We want the shah from the United States government and it must return the shah. Obtaining [him] in a political bargain contradicts our goals."

It was Khomeini's health and today's election that were at the center of Iran's concerns yesterday.

The Revolutionary Council claimed to have received reports of infiltrators from Iraq whose goal is to sabotage the election, and ordered the Revolutionary Guard militia on full alert.

Voting today is to begin at 8 a.m. and end at 6 p.m., local time, with the counting scheduled immediately afterward. If no candidate receives a majority in today's voting, a second round of balloting is to take place Feb. 8.

In his broadcast yesterday, in which, according to Reuter, he sounded quite weak, Khomeini urged all Iranians to vote, saying, "The destiny of Islam and the nation depends on this."

"Once the president is elected," Khomeini said, "the people must back him."

The official Pars news agency quoted the head of the ayatollah's medical team as saying Khomeini's heart condition was improving, and a close aide told 600 well-wishers gathered in a snowstorm outside the hospital that he was well enough to stand and pray, Reuter reported.

Hours before the polls opened today, five presidential candidates responded to Khomeini's broadcast with a pledge to support whoever is elected.

The five -- Bani-Sadr, Habibi, Ghotbzadeh, nationalist candidate Dariush Forouhar and Sadegh Tabatabai, Khoemeini's son-in-law -- issued a statement in which they promised that after the presidential election they will obey the chosen president and will be at the service of the people and the country."

In Qom, between 2,000 and 3,000 sheep and cows were reported sacrificed in the streets and outside mosques in pryer rites for Khomeini.

Eyewitnesses said thousands went to the city's mosques and holy shrine to offer special prayers for his health.