Tens of thousands of americans have sent Christmas cards to the 50 hostages in the U.S. Embassy in Iran, jamming the U.S. Postal Service's international sorting stations.

The amount of mail bound for Iran that has passed through New York, the departure point for international mail, has nearly quadrupled since Monday, officials there report.

During the 24-hour period ending at noon yesterday, the officials said, the station processed as much mail for Iran as an American town of 25,000 would receive in a day. At least 85 percent of the mail -- cards, letters and packages -- was addressed to the hostages, they said.

Postal authorities attribute the phenomenal jump in the volume of Iranian mail to pleas by a growing number of radio and television stations and newspapers that Americans demonstrate their support for the hostages by drowning the Iranian mail system in a sea of letters bound for the student-held embassy. Officials expect the deluge to grow as Christmas approaches.

"It's a tremendous amount," said a Postal Service spokesman here in Washington. "We made a decision on Friday that, even if the letters are short-paid [not enough postage affixed], we were going to put it through. We did not want those pieces of mail to end up on the dead letter pile."

Even a few packages of cookies and other goodies are being sent, according to the Postal Service's national spokesman. "It's just the American style that somebody will send a package," he said. "It's like in World War II. It's almost a tradition."

According to postal officials here and elsewhere in the country, the deluge started at the end of last week and has continued to build.

One of the earliest radio stations to begin promoting the idea was Chicago's WGN. Last Thursday, a caller to a local talk show suggested that greeting cards be sent, and within hours, the switchboards at the radio station and at post offices were jammed by telephone calls from individuals wanting to know the U.S. Embassy's address.

Locally, in a variation of the Christmas card campaign, WJLA-TV asked listeners to write to a post office box here, expressing their concern for the hostages' safety. The station said it will deliver the letters in bulk to the Iranian Embassy here.

Yesterday the station made its first mail pickup and found more than 760 letters. "That's amazing," said Lindy Spero, spokeswoman for the station. "That's just in the first 24 hours."

The call for Christmas cards has prompted others to act on their own. The Mayflower Hotel, for instance, has notified employes it will pay the postage for all letters and cards its staff of more than 600 wants to send to the hostages.

Sarah Sullivan, a math skills teacher at Arlington County's Williamsburg Intermediate School, decided on Monday that she would corner students and ask them to write letters, too.

"The least we could do for these people [the hostages] is send them a card," said Sullivan. "I'm very patrotic-- I get kind of chill bunps when I hear "The Star-Spangled Banner'-- And it just bothers me to think that this could happen."

Before the embassy takeover, the Dulles postal station received about 580 pieces of mail to Iran a day, said Turner, whose staff sorts international mail from 12 southeastern states. "Now we're getting about 3,000 pieces a day, and that's just for the hostages and doesn't count the nonhostage mail."

Letters to the Iranian Embassy are up sharply, too, according to George Conrad, spokesman for the District of Columbia post office. Typically the embassy receives about one sack of mail a day, he said. The amount has grown since Monday to between two and three sacks a day.

Locally, mail to Iran is up almost six times the normal amount, according to Edward Turner, operations manager of trhe Dulles International Airport post office.

"We expected it," said an Iranian Empassy volunteer working on the mail yesterday. "We're trying to read each piece of mail and respond to it. We're forwarding to Iran all those letters addressed to the [U.S.] embassy there."

The State Department appealed to Iran yesterday to make sure that all cards and letters addressed to the hostages are delivered. The Iraian embassy here said, it was confident that all the mail would be.

The amount of mail involved may prove to be mountainous, postal authorities said. During all of last week, one official noted 48,000 pieces of mail were shipped to Iran from JFK International Airport.

But according to Jerry Fox, the postal service's JFK general manager, more than 44,000 pieces of Iran-bound mail were handled by his staff between 8 a.m. Tuesday and noon yesterday alone. "It's not getting any smaller," he said.

Those wanting to send Christmas cards to the hostages should address their letters to: Hostages, United States Embassy, Box 50, 260 Taleghani Avenue, Ehran, Iran. Postage is 31 cents for each half ounce.