看情形而定，如果指代警局用is，如果指代警察用are。police是集合名词，谓语动词用复数，the+形容词表示一类人。例句：If you see it,ring up the police at once.你要是看到它，请立即打电话通知警察局。
例句
1、The police rounded up a number of suspects
警方围捕了一些嫌疑犯。
2、The police arrived, and so did reporters and a photographer from the 'Journal'.
警察赶到了那里，《日报》的记者和摄影师也到了。
3、I reported the theft to the police
我向警方报告了这起盗窃案。
4、The police also found a pistol
警方还发现了一把手枪。
5、Her assistant was accused of theft and fraud by the police
她的助手被警方指控犯有盗窃和欺诈罪。