TEHRAN, Iran--Iranian leaders yesterday refused to allow two U.S. envoys into Iran to negotiate for the release of about 60 Americans being held hostage by Iranian students in the U.S. embassy here.

The envoys, former U.S. Atty. Gen. Ramsey Clark and William Miller, a Senate Intelligence Committee staff member, were carrying a personal message from President Carter to the Ayatollah Ruhollah Khomeini. The letter asked for the Ayatollah's help in freeing the hostages, held since Sunday by students demanding that the United States return the exiled Shah Mohammed Reza Pahlevi to Iran for trial.

The hostages are being "pushed around, abused, intimidated and mishandled," but no one has suffered serious injuries, one U.S. official said yesterday.

The Iranian students now have new weapons, including machine guns, Hodding Carter, a State Department spokesman said yesterday. There is no evidence that shooting has occurred, he added.

In addition, U.S. government officials urged all Americans in Iran to leave the country after Iranian students seized two more hostages.

Clark and Miller will remain in Turkey indefinitely, "pending clarification" from Tehran. Hodding Carter said yesterday. Iranian officials say they will not receive the envoys unless the Shah is returned. The Shah is currently undergoing cancer treatment in New York City.

In New York stock market analysts blamed the tense situation in Iran for yesterday's decline of the Dow Jones average.

Today's drop marked the third straight day of broad market decline, pushing the Dow Jones average below 800--its lowest close of the year. Since Monday, the average has fallen 22.27 points.

Investors also remained edgy over continued reports of an Iranian oil cut off, despite denials by the White House and the National Iranian Oil Co.