Complex sentence: McNamara was highly skeptical of the SST project and savaged Halaby's predictions but was afraid the project might be turned over to the DoD, so he was careful to press for further studies.
Split into simpler sentences: McNamara was highly skeptical of the SST project and savaged Halaby's predictions, and was afraid the project might be turned over to the DoD. So he was careful to press for further studies.