In the advertisement, the Clinton campaign again portrays a family asleep in the middle of the night when the phone rings, meant to evoke a national crisis. The narrator then intones, “John McCain just said the government shouldn’t take any real action in the housing crisis; he’d let the phone keep ringing.”

Within hours, the McCain campaign released an advertisement on the Internet. It starts with images of the Clinton advertisement, with the narrator then commenting, “Hillary Clinton and Barack Obama just said they’d solve the problem by raising your taxes — more money out of your pockets.”

The advertisements highlighted how the two parties’ candidates have developed starkly different approaches to the housing meltdown, with Obama and Clinton calling for billions of dollars in aid for distressed homeowners and McCain warning against costly federal intervention.

McCain’s rapid response recalled a similar advertisement by the Obama campaign in response to Clinton’s original red-phone advertisement, which questioned Obama’s readiness to be president.

The advertisements on Wednesday capped a day in which McCain gave speeches at old haunts, from the Naval Academy in Annapolis, Maryland, to the Florida base here where he learned to fly, and revealed that he had begun drawing up a list of roughly a score of potential running mates.

McCain joked on his campaign bus in Annapolis that his list had “every name imaginable” on it and stood at about 20 people but that there were probably a hundred people who thought they were on it. As nervous aides looked on and occasionally interjected to say that no decisions had been made, McCain said he had spoken with several people about heading the search for a running mate.

He broached the subject in a radio interview on Wednesday with Don Imus. “We just started this process of getting together a list of names and having them looked at, and I don’t know how long it takes,” he said. “But if I had a personal preference, I’d like to do it before the convention to avoid some of the mistakes that I’ve seen made in the past, as you get into a time crunch and maybe sometimes don’t make the announcement right.”

Choosing a conservative running mate might help McCain energise the Republican base.

Officials who have been mentioned include Secretary of State Condoleezza Rice and several governors, like Tim Pawlenty of Minnesota, Charlie Crist of Florida, Jon Huntsman Jr. of Utah and Mark Sanford of South Carolina. Former governors have also been mentioned, including Tom Ridge of Pennsylvania, whose support of abortion rights could cause trouble among conservatives already wary of McCain, and former primary opponents, Mitt Romney of Massachusetts and Mike Huckabee of Arkansas.