看情形而定，如果指代警局用is，如果指代警察用are。police是集合名詞，謂語動詞用復數，the+形容詞表示壹類人。例句：If you see it,ring up the police at once.妳要是看到它，請立即打電話通知警察局。
例句
1、The police rounded up a number of suspects
警方圍捕了壹些嫌疑犯。
2、The police arrived, and so did reporters and a photographer from the 'Journal'.
警察趕到了那裏，《日報》的記者和攝影師也到了。
3、I reported the theft to the police
我向警方報告了這起盜竊案。
4、The police also found a pistol
警方還發現了壹把手槍。
5、Her assistant was accused of theft and fraud by the police
她的助手被警方指控犯有盜竊和欺詐罪。