More than half of the 7,700 Iranian students identified by immigration agents in the last year as deportable have failed to appear for deportation or to leave the United States when ordered to do so, according to immigration officials.

Many of them have simply disappeared, presumably going into hiding in order to avoid deportation, immigration officials say. Thousands of others have either filed for political asylum or appealed immigration court rulings against them, ensuring that they will not be deported for months -- if not years -- while their cases are waiting to be heard.

As a result, the Immigration and Naturalization Service (INS) has made so little progress in its year-long effort to deport those Iranians, most of whom are deportable because they have overstayed their student visas, that only 478 have actually been forced to return home.

In an effort to reduce the number of students who choose to go into hiding rather than appear in court to leave the country, INS headquarters here has ordered its field offices throughout the country to require deportable Iranian students to post a money bond when arrested.

Iranian students who cannot pay the bond -- which has been averaging about $2,800 will be jailed under the new order, an INS spokesman said yesterday. The bond will be returned only upon proof that the person has compiled with the final ruling of the immigration court.

In addition, the INS has ordered its district directors to use all criminal investigators, regardless of their current assignment, to help locate and deport Iranian students.

The bond requirement has caused concern among some immigration lawyers who argue that it is discriminatory.

"What they've done is set up a system whereby all those poor Iranian students who can't make the bond will end up in jail while the rich ones get to walk the street," said Michael Maggio, a Washington immigration lawyer.

Maggio also asserted that the regulation is discriminatory because it is based clearly on the fact that, because the students are Iranian, they are therefore more likely to fail to appear for a hearing than any other nationality group.

Immigration officials argue, however, that the Iranians' poor record of cooperation and compliance is sufficient proof of the need for the bond requirement. The order was sent out last month in a telegram to INS offices throughout the country.

"Reports from the field indicate little progress in effecting the actual departure from the United States of deportable Iranian students has been made," the order reads. "This is despite the fact that the Iranian student project is presently the first priority for the INS.

"All criminal investigators, notwithstanding the decision unit to which assigned, shall be considered as available to bring this project to a prompt conclusion . . . ."

According to an INS spokesman, 59,431 Iranians are known to be studying in the United States, a figure arrived at after a year-long effort to track down the students in the wake of the seizure of the American hostages in Iran. Of that number, 7,736 have been identified by immigration service investigations as deportable. More than 4,000 of these Iranians have failed to appear for deportation hearings or to leave the U.S. when ordered to do so.

In INS immigration court proceedings over that same period, 2,287 of those students actually have been ordered deported by immigration judges while 1,202 others have had their student status reinstated. An additional 2,606 have filed for political asylum, arguing that their lives would be in danger were they forced to return to Iran. More than 51,000 Iranians have been identified as being in the U.S. legally.

The slowness of the effort has caused some bitterness among those concerned about enforcement of the nation's immigration laws.

"Just as the hostage problem shows the impotence of American foreign policy, the inability to cope with the Iranian students who are in this country illegally points up the utter impotence of our immigration laws," said Roger Conner, director of The Federation for American Immigration Reform.