Andy Hayman, assistant commissioner of the Metropolitan Police, said building ties started from a low baseline.
"We have close links with the Muslim community but the next step is getting them to share information," Hayman was quoted as saying in an interview with The Guardian.
"I fully understand how difficult that is, the repercussions of arrests and so on, but that has to be weighed against the mass loss of life that could result from further atrocities."
Hayman added that London was a "prime target" for further attacks.
"I don't want to scaremonger but it has to be said, when you look around the world and at the prominence of London, that the threat is real," he said.
Four bombers killed 52 Underground railway and bus passengers on July 7, and four other men staged a series of failed attacks two weeks later.
Hayman said police were monitoring a number of suspects, but none is believed to be directly related to the July attacks.
Also Thursday, officials said they had mailed out the first offers of compensation to victims of the July 7 bombs.
"The first offers of awards have gone out. We have posted the offers and I think more will go out in the next few days," said Howard Webber, chief executive of the Criminal Injuries Compensation Authority. "Once we get acceptances the checks can be dispatched by return of post."
Lawyers for some of the injured and bereaved have complained that compensation payments were taking too long to reach victims struggling to pay bills and meet medical costs and other expenses. On Sunday, Prime Minister Tony Blair promised that checks would be in the mail soon.
Victims and their families are eligible for payments of up to 500,000 pounds ($885,000, euro735,000).
The agency said it had received 183 applications for compensation from injured people and relatives of those killed. Some 750 people suffered injuries in the attacks, 350 of them serious enough to require hospital treatment.