By BARBARA CROSSETTE

NITED NATIONS, Feb. 7 -- With a new arms inspection system
now being devised for Iraq, some arms control experts are looking
anew at Iraqi biological weapons programs and finding evidence of at
least one more secret project still to be uncovered.

In recent months, Milton Leitenberg, an expert
on biological weapons, has been looking at this
murkiest and most dangerous corner of Saddam
Hussein's armory. He says a series of reports
add up to indications that Iraq may be trying to
develop a new viral agent, possibly in
underground laboratories at a military complex
near Baghdad where Iraqis first chased away
inspectors six years ago.

Mr. Leitenberg, a senior fellow at the University
of Maryland's Center for International and
Security Studies, has collected reports on Iraqi
sites and activities from a variety of people,
including two Iraqi defectors.

In Britain, research and intelligence experts, also
convinced that there are more germ warfare
agents left in Iraq than previously known, have
suggested that Iraq may have produced the
organism that causes bubonic plague. But no
evidence has been published in support of this
theory, American experts say, and United
Nations inspectors found no trace of the plague
in Iraq.

Mr. Leitenberg, who does not know what the new virus is -- if indeed it
is a virus and not a bacterial agent -- said in an interview that
accumulating evidence of this previously unknown component of the Iraqi
germ warfare program suggests that Hans Blix, the new chief inspector
for Iraq, may want to give priority to biological weapons. Mr. Leitenberg
and other experts also say inspectors will have to be aggressive in
demanding access in Iraq. Dozens of major questions remain
unanswered.

The elimination of biological weapons in Iraq may be as important -- or
more important -- to the Iraqi people as to the outside world, scientists
say. Experts working with the United Nations Special Commission, the
first disarmament body created for Iraq after the Persian Gulf war, said
some of the bacterial and viral agents Iraq was producing then were of
little use for war. Among them were aflatoxin, a fungal agent that can lead
to liver cancer, and rotavirus, which causes diarrhea in children and the
elderly.

Experts say agents like these were more probably intended for use
against Iraqis. Mr. Hussein did not shrink from using chemical weapons
on Kurds in 1988, and some scientists and physicians say he may also
have tried aflatoxin.

Iraq told United Nations inspectors that it tested mixes of aflatoxin with
various nerve gases and other agents in 1989. Research being done
among Kurds in Europe has turned up some liver cancer figures higher
than expected, a former inspector said.

Mr. Blix is the chairman of the new United Nations Monitoring,
Verification and Inspection Commission and thus chief inspector for Iraq.
From 1981 to 1997, he was director general of the International Atomic
Energy Agency, which was responsible for dismantling Iraq's nuclear
programs.

In March, he will take over inspections of biological, chemical and missile
programs, and he has been asked by the Security Council to give Iraq a
list of tasks it must accomplish to have international sanctions suspended.

Iraq has not said it will admit inspection teams, though; it says it has
already fully disarmed.

At a news conference on Friday, Mr. Blix said there were very few
unanswered questions on Iraq's nuclear arms. In the missile area, Iraq
may also be able legitimately to meet demands for closure. Chemical
programs have some outstanding questions on quantities of poison
produced, especially the nerve agent VX, and whether those substances
were loaded into warheads.

Biological programs, however, have been the most difficult to uncover.
Richard Butler, the former executive chairman of the United Nations
Special Commission, said that is because they are the most important to
Mr. Hussein.

"Over nine years now," he said in an interview last week, "Iraq has
consistently made extraordinarily strenuous efforts to hide the biological
program -- well beyond those they made on missiles or chemicals. Why?
Why? No effort was too much to prevent us from getting to the truth.
That says to me it was big and nasty."

Iraq is required to be certified free of weapons of mass destruction
before the United Nations lifts sanctions that were imposed because of
the invasion of Kuwait in 1990. Arms control experts contend that the list
of conditions for suspending sanctions must be left open-ended so
inspectors can add to it if necessary.

Otherwise, they say, Iraq will probably conceal all the activities it can
while providing minimum information to meet requirements.

United Nations inspectors from the former commission list a host of
biological agents found in Iraq, including botulinum toxin, anthrax, camel
pox and infectious hemorrhagic conjunctivitis virus. The commission was
never able to account for all the stocks of biological agents -- which Iraq
denied having until 1995 -- or for large amounts of growth material used
to produce germ warfare agents.

Iraq is also able to make its own growth media, scientists say. Mr.
Leitenberg, who has produced a preliminary paper on his suspicions
about a new virus program for the Institute for Science and International
Security, an independent research organization in Washington, said
missing bacterial growth media could be irrelevant because viruses can
be grown on tissue culture or fertilized eggs, and Iraq has many
incubators.

In interviews this week, Mr. Leitenberg said new evidence from Iraqi
exiles, one an engineer, and from other pieces of information assembled
and analyzed by experts leads to a renewed focus on an Iraqi site known
as Salman Pak, an area of about 10 square miles in a bend in the Tigris
River southeast of Baghdad.

The area once housed a large military research institute and animal testing
centers and was always of great interest to inspectors. Although Iraq said
it had relocated its research laboratories to Al Hakam, a complex later
destroyed by the United Nations commission, Salman Pak was bombed
in 1991 during the gulf war, an indication that Western intelligence still
considered it an active installation.

Mr. Leitenberg said an underground laboratory might still be functioning
there, detectable by ground-level air ducts camouflaged by a small shed.
He said a United Nations inspector had missed an above-ground
laboratory there in 1992. A team that toured the same building in 1994
found a decontamination shower and airlock doors, hallmarks of a
high-risk environment.

About the same time, the United Nations inspectors tried to excavate a
recently dug and refilled trench at Salman Pak, looking for something that
may have been hastily buried. The digging met what inspectors call a
nearly hysterical Iraqi reaction. Iraqi officials called in mullahs to declare
the land sacred and off limits.

The inspectors never pushed hard to do more excavations there or in
nearby locations. Before the end of 1994, Iraq had forced a crisis with
the United States by moving troops to the border with Kuwait again.

In the following months, the inspectors finally cornered Iraq into
confessing to the biological weapons program it had said it never had,
and Salman Pak became less a site for detective work than for
verification of documentation turned over by the Iraqis. Arms experts
want the detectives to go back.