Any new U.S. effort to counter the long-term threat from Iraqi weapons of mass destruction could face substantial political and economic obstacles, according to specialists on the Middle East and several U.S. legislators.

Secretary of State James A. Baker III suggested such an effort several weeks ago to peacefully resolve the regional security problems raised by Iraq's invasion of Kuwait.

"We're going to make sure, to the best of our ability, that {Iraqi President Saddam Hussein's} military machine, and also his chemical and nuclear capability, {will} be denied him," Vice President Quayle said yesterday morning.

President Bush told Congress recently that an embargo on sales of key weapons technology and equipment to Iraq would last "long after all our troops come home."

But any attempt to expand the existing United Nations-sanctioned trade embargo to encompass long-term nonproliferation measures aimed at Iraq and other Persian Gulf nations may be politically difficult, experts say.

They say that perhaps the biggest obstacle is Israeli possession of nuclear arms, and possibly chemical weapons as well, a circumstance that makes neighboring countries such as Iraq reluctant to abandon efforts to offset this by acquiring their own advanced weapons.

Quayle said on ABC-TV's "Good Morning America" that the Bush administration believes that if Saddam were toppled his successor would be just like him.

Other potential impediments include recent Iraqi acquisition of chemical and missile know-how that sharply reduced its dependency on foreign suppliers, and the longstanding inability of the United States and other Western nations to ensure rigid compliance with nonproliferation measures.

Rep. Lee Hamilton (D-Ind.), chairman of the House Foreign Affairs subcommittee on Europe and the Middle East, praised Baker's idea, saying that "it doesn't take the cooperation of 150 nations, but of four or five key {allies}" that sold arms technology to Iraq in the past.

But Rep. Stephen J. Solarz (D-N.Y.), chairman of the House Foreign Affairs subcommittee on Asian and Pacific matters, said Baker's "formula consists of a large measure of vagueness seasoned with a healthy dose of wishful thinking. . . . It's very difficult for me to imagine how you would negotiate such a security arrangement."

State Department officials said the United States will probably work to strengthen existing controls on sales of nuclear-, chemical-, and missile-related equipment coordinated by loose confederations of Western nations, by seeking wider participation from former East Bloc countries and promoting tougher enforcement of the controls.

Baker noted that "Iraq was militarized by France and the Soviet Union," which now support the U.N. trade embargo. "I think what's happened here will make it very, very plain to a number of countries that were not really committed to nonproliferation efforts that it's damn important," he said.

But several independent experts note that a major nonproliferation measure, the eight-nation Missile Technology Control Regime (MTCR), lacks any enforcement mechanism and has had only limited success in stemming Middle East imports of missile equipment and know-how.

"If anything, Third World domestic production of missile systems has increased since 1987," when MTCR was unveiled, reported King's College analysts Martin Nevias and Darryl Howlett recently for the International Institute for Strategic Studies in London.

Iraq's missile program is run from a modern, $200 million research complex near the northern city of Mosul and includes a fledgling capability to make solid-fuel propellants, according to several experts. Iraq has also developed and tested engines for medium-range ballistic missiles, albeit highly inaccurate ones.

A separate 20-nation organization, the Australia Group, formed in 1984 to monitor and control the export of chemicals used in poison gas weapons by Middle East nations, has a "mixed record," according to Seth Carus of the Washington Institute for Near East Policy. "Although its activities made it more difficult to obtain key precursor" chemicals needed to make mustard gas and nerve agents, he said in a recent report, "countries intent on acquiring such chemicals can still do so."

Key Iraqi poison gas factories were constructed after 1984 with help from West German and Swiss firms in what Central Intelligence Agency director William H. Webster has called a concerted Iraqi effort "to make its program entirely independent of foreign suppliers."

But several experts add that Iraq's nuclear bomb-building program remains dependent on external assistance and likely would be vulnerable to a concerted nonproliferation effort. Iraq has bought equipment to produce highly enriched weapons-grade uranium, but needs more material to begin production, and is considered unlikely to have its first bomb for at least five years, according to Leonard S. Spector of the Carnegie Endowment for International Peace.

"Rolling back" Iraqi chemical and nuclear capabilities under some new regional accord as Baker called for is considered unlikely as long as Israel maintains its own nuclear arsenal and most Arab states shun direct negotiations with Jerusalem, other experts said.

Egyptian, Syrian, and other Arab representatives at a January 1989 international chemical weapons conference flatly equated Israeli possession of nuclear arms with the right of other nations in the region to stockpile poison gases, the so-called "poor man's atomic bomb."

"In Egypt and Jordan, you cannot . . . mention arms control without them saying, 'Fine. But now let us agree that nuclear weapons will be on the table' {and} this poses problems for the Israelis," said former National Security Council aide Geoffrey Kemp, who recently toured the Mideast with other nonproliferation specialists.

"Most people agree that any hope of getting a comprehensive package that puts all these items together and reaches any conclusions is indeed pie in the sky," Kemp said.

Finally, several critics say the Bush administration's opposition to mandatory trade sanctions against illicit proliferators may undercut any new diplomatic effort. They cite Assistant Secretary of State John H. Kelly's testimony to the Senate Foreign Relations Committee a few weeks before the Kuwait invasion that automatic sanctions would unjustly interfere with U.S. trade and "would not improve our ability to exercise a restraining influence on Iraqi actions."

Officials said that despite the Iraqi invasion, the State Department opposes the Senate-passed Chemical and Biological Weapons Control Act, which automatically severs U.S. government contracts with firms that illicitly export chemical-related equipment, and halts U.S. trade with nations that have used chemical weapons. "If anything, the invasion of Kuwait proves the need to maintain flexibility," a State Department spokesman said without elaboration. "We haven't changed our opinion."

One administration official, acknowledging the difficulties, said that at the State Department, "there probably remains a hope rather than an expectation that this plan will work. The alternative {military action} looks too grave not to at least entertain the idea."