The engineer who supervised the just completed $1.5 million repairs at Wolf Trap's Filene Center, where a nine-foot crack was discovered in a steel support beam four months ago, said yesterday he could not guarantee that another mishap will not occur in very cold weather.

However, he said it was highly unlikely that the center would face a similar problem during the performing arts center's summer season, scheduled to begin June 11.

"It's very, very unlikely that there is any possibility of . . . a fracture during the summer season," said the engineer, O. Charles Guedelhoefer, during a press conference yesterday. "But until the metallurgical tests come back, I can't say definitively that it won't happen again at negative 6 or negative 7 degrees below zero."

The dramatic, two-inch-wide crack was discovered Jan. 24, days after a severe cold snap paralyzed the metropolitan area. After tests were performed at Lehigh University in Bethlehem, Pa., in February, engineers concluded that the crack was caused by a combination of factors, including cold temperatures, wind, a welding flaw and poor metallurgy.

The fissure caused the Filene Center's roof to sag visibly, and in April engineers used a hydraulic jack to boost it nearly 10 inches to its original height. Scaffolding helped buttress the roof until last month.

Yesterday, workers were readying the stage set and cleaning up the building in preparation for the season opener, which features Beverly Sills and the New York City Opera. Signs posted around the building warned: "Hard Hat Area."

The Filene Center is the centerpiece of this country's first national park for the performing arts. Officials for the Wolf Trap Foundation, which handles programming at the center, said ticket sales for the summer's 11-week season are well ahead of those in past years.

In addition to repairing and reinforcing the 130-foot-long beam where the crack was found, workers have tested, inspected and upgraded welds throughout the $18 million structure.

Guedelhoefer, a principal with the Chicago-based structural engineering firm of Raths, Raths and Johnson that was hired by the Wolf Trap Foundation to supervise repair work, said $200,000 of the $1.5 million repair bill was spent on inspections and quality control.

Guedelhoefer called the repairs "very complex" and "very successful," and said the work "greatly minimized the chance of recurrence." He said about a dozen subcontractors worked on the repairs.

Guedelhoefer said he is awaiting results on more than 100 test samples that will determine the beam and weld metallurgy -- essentially the recipe by which steel is made.

The initial repair bill will be paid in large part by the Kemper Life Insurance Co., which represents the Wolf Trap Foundation, and by some of the subcontractors who rebuilt the Filene Center after it was destroyed in a 1982 fire, Guedelhoefer said.

Guedelhoefer would not say how the costs would be divided, but he said lawsuits are likely among the various contractors and insurance firms to sort out liability.

The companies involved in the rebuilding of the center include Dewberry & Davis, the Northern Virginia architectural and engineering firm that designed the Filene Center and specified the materials used in the welding and beam; Globe Iron Construction, a Norfolk concern that fabricated the beam; Materials Testing Laboratories, also of Norfolk, which tested the welds; Bethlehem Steel of Bethlehem, Pa., the steel supplier, and G & C Construction of Vienna, the chief contractor.