Daily the crowds gathered outside the U.S. Embassy here chanting "Death to the shah, death to Carter," as the voice from the loudspeakers mounted on the embassy walls whips them into ever greater fury.

Outside, the atmosphere is like a campus on the day of a big game, but those inside the embassy, where about 60 Americans are being held hostage, are anything but innocent cheerleaders.

Unsmiling and wise to the ways of the contemporary world, these latter-day devotees of 7th century Irann have proven themselves past masters of the uses and abuses of the mass media, and every bit as disciplined as the U.S. Marines they hold as hostages.

Only in the past several days has a clear picture begun to emerge of what is going on inside Henderson High -- as the main embassy building is named because its brick colonial architecture, built under Ambassador Loy Henderson in the 1950's, looks like the classic American high school.

Even that picture is a blurred one, based on the limited reports of foreighn diplomats who have been allowed brief glimpes of the hostages and on the experience of journalists who have been allowed to enter only a small part of the embassy compound.

The foreign diplomats who have seen the hostages report that their physical health is as good as could be expected but that they are under considerable mental strain. They are bound hand and foot, night and day, and have to be spoon-fed by their captors.

Little more has been made public about the fate of the Americans -- diplomats, Marine guards and other embassy personnel. About the 400 Iranian militants who seized the embassy last Sunday, however, more is emerging.

There are both deadly serious and comic touches at the same time.

Outside the embassy one banner lost a little something in translation to English: "Iran was like a kidney for America. With the help of our leader, Imam Khomeini, we have severed this vital link."

For those inside the embassy, there are no such fear of Americans. The hard-eyed men and women holding the compound have handled the press readily, keeping it bottled up in the motor pool, which is on one side of the compound. All requests to visit the hostages have been denied, although one blindfolded man, his hands tied behind his back, was paraded in front of the screaming, surging crowd several days ago.

Journalists must show their press cards, which are carefully noted by name and number on a neat sheet of paper. The reporters are frisked before being allowed to enter the motor pool area.

Nevertheless, evidence is growing that those masterminding the embassy takeover are experienced in the ways of the world press and know how to get their message across. Amid all the posters and slogans plastered on the embassy wall in one neat spot carefully reserved and labeled in English: "For Reporters and Mass Media Correspondents." Notices of new conferences and other announcements appear regularly here.

And once a news conference is under way, the spokesman's very agility at fielding even the nastiest questions has prompted suggestions that not everyone is, as advertised, a student from Tehran University.

Some Iranians watching television footage depicturing events inside the compound have remarked that some of the group's leaders looked older -- and acted more mature -- than students.

In fact, in the week since the embassy takeover, there has been speculation that various outside groups have fought to get a piece of the action.

Some of the men heard by visitors to the embassy compound were speaking to each other in Arabic -- apparently to prevent other Iranians from understanding their conversation -- prompting suggestions that they might have been Iranian revoluationaries trained by Palestinian guerrillas in Lebanon.

Important clerics, such as Revolutionary Guard commander Ayatollah Hassan Lahouti, also have been seen inside the compound.

"A lot of people have had fingers in the pie from the begining and it's not over yet," a diplomat said. One close observer claims the extreme left had planned the embassy attack but was beaten to the punch by the Islamic fundamentalists.

The sophistication of the group inside the embassy extends to the arguments they have mounted in defense of holding diplomatic personnel hostage in violation of every known rule, of international law and diplomatic practice.

By putting on a display of walkie-talkie metal detectors and other nondescript bits of technology, they have built a case that the embassy was really a "den of espionage" and that those inside were spies who have lost their immunity.

"American spies must be executed," said one sign outside the embassy. Purported official documents found inside the embassy have been pictured as yet more evidence of espionage activity.

Outside the embassy walls, the crowds grow daily. For the first time today, the regulars on Telaghani Avenue were joined by a group of construction workers who rolled up in Mack trucks and sported yellow plastic hard hats. Later, a small detachment of blue uniformed Air Force cadets arrived. Pajamaclad Revolutionary Guards, back from the fighting in Kurdistan and wearing bandages to prove their combat experience, were given a warm welcome.

With an eye to the television cameras, various banners give a flavor of the times -- often in English. One proclaims: "1942: Khomeni said the U.S.A. is worse than Britain, Britain is worse than thee U.S.S.R. and the U.S.S.R. is worse than those two. Each is filthist (sic) than the other."

Underneath in smaller print is the current update of the original which condemned Allied intervention in Iran. It said, "But today our fight is against the U.S.A."

If nothing else, the embassy has become something of a tourist attraction. Braving the crowds and blaring slogans, a young Englishman named Keith Mooney, on his way to Pakistan, showed up just as a group of Moslem fundamentalists began praying in the motor pool.

"Sure put Iran back in the news," he said.

He seemed oblivious to the potential danger to foreigners, which has prompted West Germany to close its embassy and ordered about 1,500 of its citizens to leave what was offically described as a "dangerous situation."