Portugal is to ask Nato for help with security - including Awacs surveillance planes - during the Euro 2004 football championships in June.
Nato Awacs aircraft have been used to help cover large events
Prime Minister Jose Durao Barroso told parliament every effort was being made to protect people but there were still no credible threats against Portugal.
Portugal has tightened its security measures since the 11 March Madrid train bombings in neighbouring Spain.
Around 1.2 million fans are expected at Euro 2004's 31 games.
During the football championships in June, and the huge Rock in Rio music festival in May, Portugal will restore border controls it scrapped in 1991, reintroducing passport checks and vehicle searches.
It has already strengthened security in key transport areas and at main public buildings, including foreign embassies.
Around 1.2 million fans are expected at the football's competition's 31
Mr Durao Barroso told parliament that Portugal's Ambassador to Nato in Brussels was due to deliver a formal request later on Thursday.
Defence Ministry spokesman Miguel Guedes said there were no plans to ask Nato for help beyond the Awacs aircraft.
"It's a very specific request for planes for that specific period," he told AP. "It's
basically to help monitor Portuguese airspace over a much wider area than normal radars cover and to report anything unusual."
Other countries have asked Nato for support for large events such as the 2002 Winter Olympics in Salt Lake City and political summits in Europe.
Greece has asked Nato to share intelligence on potential terror threats and increase Mediterranean naval patrols, as well as help patrol its airspace, during the Olympic Games in Athens this summer.
Mr Durao Barroso also called on the European Union, whose leaders are meeting in Brussels, to step up the fight against terrorism.
"Just like Nazism in the past, terrorism is now the big threat to our civilisation but I am certain that democracy, freedom and peace will once again triumph," he said.
"I am certain that Portugal will be in the front line, as it should be, of the fight against terrorism. This is in our interest and our interests correspond to our values."