"派警察监视" can be translated into English as "deploy police officers to monitor" or "send police to keep watch over".
Both expressions convey the idea of assigning police personnel to observe or oversee a particular situation, individual, or area. Here are some example sentences to illustrate their usage:
1、 The authorities decided to deploy police officers to monitor the suspect's movements.
（当局决定派警察监视嫌疑人的动向。）
2、 To ensure safety, they sent police to keep watch over the protest site.
（为了确保安全，他们派警察去监视抗议现场。）