FAIRBORN, Ohio — An unusually high level of security is expected to be continued for at least two weeks at Wright-Patterson Air Force Base near Dayton, authorities said Monday.

        After “a credible threat to a specific target on base” last Tuesday, security was pushed to its fourth and maximum level, “Delta” — thought to be a first at the base, two spokeswomen said Monday.

        The base was on “lockdown,” with no visitors allowed. Officials wouldn't give further details, but said the threat subsided and the security level was reduced one level, to “Charlie,” Thursday afternoon.

        That security level, rarely invoked, remained posted on yellow signs at base gates Monday. Personnel wore camouflage combat fatigues; “non-mission-essential” personnel stayed home. Some gates were closed; at others, traffic was backed up for a mile or more as guards thoroughly checked identification and bags.

        “We will probably remain in this threat condition for some time to come,” said Gen. Lester L. Lyles, commander of the Air Force Materiel Command, which manages Air Force supplies and equipment. “Our intelligence reports tell us (the Sept. 11 attacks were) not an isolated incident; there could be more to come.”

        Malls, airports and amusement parks could be “potential targets,” he said.

        Gen. Lyles addressed an audience of about 70 military and civic leaders who were participating in a previously scheduled town hall meeting that took on added significance because of last week's terrorist attacks.

        After considering canceling the event, Air Force officials realized “more than ever, we need to stand up and let you know what's going on at Wright-Patterson,” said Lt. Gen. Dick Reynolds, commander of the Air Force Aeronautical Systems Center at the base.

        The commanders discussed the Air Force's role in Operation Noble Eagle, the military's response to the deadly terrorist strikes.

        They also said the Air Force has accelerated development and testing of advanced “uninhabited” stealth aircraft and a “casualty location and assessment device” that can detect human life signs in up to 30 feet of solid concrete.

        “That device has been sent into the "war zone,'” Lt. Gen. Reynolds said, referring to the demolished World Trade Center in New York. However, as of Monday, he did not think the prototype device had yet been used in search efforts there.

        Gen. Lyles said the Air Force is doing “a lot of things that are visible and some things that are not visible.”

        The 311th Human Systems Wing, “the Air Force's SWAT team for chemical and biological incidents,” is on standby, Lt. Gen. Reynolds said.

        Air Force planes are patrolling 15 major cities and more planes are stationed at 26 secret locations, ready to respond. The goals are to protect the homeland, high-value resources and monuments, and to intercept and destroy any hostile aircraft.

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