Michael Dukakis' challenge to debate George Bush on foreign policy and defense is the Democratic presidential nominee's confident counterattack in an area that could be either a weakness or a weapon for him.

Dukakis' staff seemed taken aback by Bush's claim last week that Dukakis would unilaterally disarm the nation, an unusually aggressive attack at this early stage of the general election campaign."Shrill" was the way Dukakis described it as he delivered a series of escalating responses ending in the call for a mid-September debate on the issue.

It had already been clear, however, that Bush would strive to paint Dukakis as inexperienced and out of step on national security matters as the vice president moved to recover from a substantial deficit in the polls.

Foreign policy, defense and national security concerns are widely regarded as the weakest areas for Dukakis for a variety of reasons. It is the one area in which Dukakis, a statehouse politician, has no record. And despite his familiarity with several languages, Dukakis is not a veteran traveler to foreign capitals.

Bush, for all his image problems, can point to his experience in the international arena even before his vice presidency as ambassador to China and CIA director.

But Dukakis has been hammering away at Bush on the foreign affairs missteps of the Reagan administration. The Dukakis campaign clearly believes that Bush is vulnerable on the Iran-Contra affair, dealings with Panamanian strongman Manuel Noriega, the Pentagon contracting scandal and other problems.

Dukakis raised that criticism to a new level on Friday while campaigning in California when he said Bush doesn't "have what it takes" to run the country.

"Anybody who sits there and does nothing while we trade arms to the Ayatollah, and says he didn't know that Noriega was doing drugs and running drugs (and) is a suspected murderer, and went to the Philippines in the early '80s and commended (Ferdinand) Marcos for his commitment to democracy, in my judgment doesn't have what it takes to lead this country when it comes to foreign policy," Dukakis said.

In attacking the Democratic nominee, Bush pointed to Dukakis' opposition to some new systems, particularly land-based nuclear weapons. Dukakis has said he doesn't rule out modernization of the land-based arsenal - that is, producing a new type of missile. Yet he opposes current options - the MX and the smaller Midgetman.

Dukakis aides point to his support for other systems, such as the new Trident submarine-based missile and cruise missiles, and for development of the bomb-carrying Stealth aircraft.

Dukakis generally prefers to talk about his plans to beef up conventional forces, although he has not been specific on how to pay for expensive upgrades in equipment, weaponry, supplies and training. It is on conventional forces that he can be expected to focus if he gets that debate with Bush.