WASHINGTON -- The gas mask -- grotesque symbol of the Persian Gulf war -- has yet to be required in the conflict that now has entered its 13th day. But military experts are convinced the need will arise once the U.S.-led alliance shifts its primary thrust from air to land offensive.
"The probability is very high that Saddam Hussein will use chemical weapons against our ground forces," said Elisa D. Harris, an expert in chemical and biological warfare at the Brookings Institution.
"Not only does he have chemical weapons, but he showed in the war with Iran that he was prepared to use them, especially when facing superior ground strength, such as [Iran's] 'human wave' attacks."
Military experts say a ground war will bring allied troops within range of accurate artillery and rocket fire, and possibly bombing by aircraft -- all of which can deliver not only conventional warheads, but also can project chemical or biological agents into the front lines of opposing troops 20 to 40 miles away.
Experts say the chemicals Iraq would most likely use are mustard gas and two nerve agents, Sarin and Tabun -- each of which it used against Iran.
It is not generally known if Saddam Hussein also possesses a third, more dangerous nerve gas known as VX, which, according to Ms. Harris, is known so far only to be in the arsenals of the United States and Soviet Union.
She expressed fears that the United States -- not Iraq -- may trigger a "chemical war," citing the Pentagon's decision to authorize U.S. forces in the gulf to use tear gas.
"If we were to be the first to use riot-control agents against Iraq, we would be giving Saddam legal justification for use of chemical weapons," Ms. Harris said.
She said only a few countries supported the United States' view that riot-control agents, or tear gas, are not chemical weapons prohibited by the 1925 Geneva protocol. Some countries, she said, may regard a chemical retaliation by Iraq as justified if the United States were to use tear gas first.
A Pentagon spokesman, Capt. Sam Grizzle, dismissed Ms. Harris's contention.
He said tear gas would be used only in "a defensive military mode to save lives, such as search-and-rescue operations," and not as an offensive weapon.
Ms. Harris said, however, that the use of tear gas has escalated into chemical warfare in nearly all wars where it was used, excluding Vietnam and the U.S. operation in Panama in December 1989.
Given the demeanor of Saddam Hussein, she said, he could be expected to retaliate with chemicals.
Chemical weapons, though terrifying, are not considered to be necessarily more harmful than conventional explosive warheads, some experts believe.
Mustard gas causes severe blistering within hours of coming in contact with human tissue, the most danger being to the lungs, which are said to be 100 times more sensitive to poison than other parts of the body. It is lethal in extreme cases, she said, but is primarily used to disable.
Nerve gases are chemically akin to pesticides, and attack the human nervous system in three stages, first causing excessive salivation, runny nose, tight chest and dim vision. This would be followed by headache, dizziness, sweating, nausea and involuntary urination and defecation. The final stage produces convulsions, muscle spasms, coma and, if left untreated, death.
The efficacy of nerve gas depends largely on how long it remains in the area as a contaminant, Ms. Harris said.
Sarin, for example, can remain dangerous for up to several hours. VX can persist for days or weeks, depending on weather conditions.
"If troops are well-trained and well-equipped to deal with chemical or biological attacks, the effects can be quite marginal," she said.
Her view was supported by Christopher Foss, editor of the authoritative London-based publication Jane's Armour and Artillery.
"When you get into close combat, it all depends on which way the wind is blowing," Mr. Foss said.
"You could end up poisoning your own troops."
Anxiety, fear of the unknown -- reactions of terror -- are the primary hazards of chemical warfare, said Chuck Dasey, spokesman for the U.S. Army's Medical Research and Development Command at Fort Detrick, Md.
"Part of the defense is to train our people to use the [protective] equipment and to know what to expect," he said.
Ms. Harris said U.S. troops in the gulf were well-equipped to survive a chemical or biological attack: The masks, impervious clothing, gloves and boots were "completely adequate" to prevent any known chemical agent or bacteria from being inhaled or coming in contact with skin, she said.
In addition, each soldier has been issued syringes and drugs to ward off the effects of nerve gas: atropine to fight off the early effects; pralidoxine chloride to restore the internal chemical balance; and Valium to counter nausea.
U.S. troops also have sealed towelettes, saturated with a compound that neutralizes mustard gas, and which can be used to wipe the chemical from their clothing and equipment.
Less is known about Iraq's capability for biological or germ warfare, as there has been no confirmed use of bacteriologic weapons in any war.
U.S. intelligence officials have long claimed that Mr. Hussein was developing biological weapons. Last week, the Pentagon said DTC "baby milk plant" that allied aircraft bombed near Baghdad was actually a disguised germ warfare facility.
Typhoid, cholera, anthrax and botulism are among the diseases that Iraq is believed to have been trying to work into weaponry, Ms. Harris said.