When Middle East expert Geoffrey Kemp participated in White House briefings on Lebanon crises early in the Reagan administration, a dimension was missing.

Having visited Beirut, Kemp realized that the typical two-dimensional map and even satellite photography used in the briefing sessions had failed to convey the extraordinary significance of terrain in Lebanon."I was astonished at how little I understood the importance of the topography surrounding Beirut - the dominance of the mountains in the conduct of everyday operations, the significance of the various ridge lines, hills and valley. Such terrain features have an impact on people's perceptions and their behavior."

Kemp, now at Washington's Carnegie Endowment for International Peace, demonstrates his view by displaying a computer-generated three-dimensional map of strategic sections of Israel.

"What this map vividly shows is why control of the Golan Heights and portions of the West Bank is critical to Israel's security," he explains. "Conversely, it helps clarify why the Arab states feel threatened by Israel's strategic posture. And it shows why these issues are so sensitive in any lasting Arab-Israeli territorial settlement."

Through the versatility of the computer, the perspective on such a map can be switched to depict the same geographical feature from the viewpoint of every competitor in the conflict - the Golan Heights from the Syrian side or the West Bank from the Jordanian side.

Such maps can be overlaid with up-to-date satellite data on the location of roads, settlements, security zones, water systems, airfields and military installations.

The maps help give policymakers a better grasp of the complexities of regional conflicts, Kemp says. The Israel map was prepared as a pilot project for a Carnegie study of arms proliferation in the Middle East.

Because of continuing computer advances, these maps can be produced more efficiently. They are increasingly being created for selected international trouble spots, according to State Department and Army officials.

Not limited to political situations, such mapping already has been used extensively for oil and gas exploration, giving experts greater confidence in their decisions about where to drill.

Digital terrain-modeling, as the mapping system is called, still involves a time-consuming process of putting into digital form all essential data about land contours, longitude, latitude and elevations.

But "once the digitized information is in the computer, you can tilt the model to change the viewing angle from 0 to 360 degrees, the viewing distance from close up to far away, and the viewing altitude from ground level up or down," says PohChin Lai, associate professor of geodetic science and surveying at Ohio State University. She produced the Israel map for the Carnegie Endowment while working at the University of Maryland.

Technically these maps "are 21/2 dimensional because a three-dimensional model is being projected onto a flat piece of paper," Lai explains. "To be truly three-dimensional, they'd have to be holograms."

Adds John B. Garver Jr., National Geographic's cartography director, "Once you build a three-dimensional model, you are able to rotate it and see the other side of the mountains." Such a model also can depict the Grand Canyon-like underwater landscape of California's Monterey Bay.

True three-dimensional mapping can portray the range of ocean temperatures at various depths or the level of atmospheric pollutants at various altitudes, says Dennis Smith, eastern regional manager of Dynamic Graphics, which recently developed the computer software for producing the maps.

Cartographically, real three-dimensional mapping is the next best thing to being there.