UEFA, who also fined the club 30,000 euros (£25,796.47), said that under new rules introduced in July, a partial stadium closer was now the minimum sanction for any incidents involving racist behaviour.
Legia's next home match is the Champions League playoff second leg against Romanian champions Steaua Bucharest at the Wojska Polskiego stadium on August 27 when the Zyleta, or north stand, which houses their hardcore fans, will remain shut.
The incidents happened in the second qualifying round tie against Welsh side The New Saints, UEFA said.
"The fight against racism is a high priority for UEFA," added UEFA. "The governing body has a policy of zero tolerance towards racism and discrimination on the pitch and in the stands.
"All forms of racist behaviour are considered as serious offences against the disciplinary regulations and are therefore sanctioned accordingly."
Legia, European Cup semi-finalsts in 1970, are attempting to qualify for the Champions League group stage for the first time since 1995-96 when they reached the quarter-finals.
The new anti-racism rules were approved by UEFA's executive committee in May. A second offence by supporters will lead to a full stadium closure for the following European match and a 50,000 euro fine.
Racist behaviour by players or officials leads to a minimum 10-match ban.
Under the same rules, Croatian champions Dinamo Zagreb played their tie against Sheriff Tiraspol at a partially closed stadium for racist chanting by fans in a second qualifying round tie against Fola Esch.
(Editing by Ed Osmond)
