The Clinton administration is planning to protect up to 4 million acres of open space in the West by creating a new class of protected public lands, tentatively called national landscape monuments, Interior Secretary Bruce Babbitt said yesterday. Babbitt said he hoped Congress would act to protect the areas under consideration, but if it does not, President Clinton could unilaterally declare the lands as national monuments. About a dozen sites are being looked at, including Steens Mountain in Oregon, the Canyon of the Ancients in Colorado, and a stretch along the Missouri River in Montana. Babbitt said the nation needs to act soon to protect disappearing open space. The new monuments would be overseen by the Bureau of Land Management.