BERLIN (AP) _ The agency charged with investigating files kept by the former East German spy agency says it expects the United States will eventually hand over secret files that were spirited away to Washington shortly after the Berlin Wall fell.

``We can't and don't want to withhold this information from the public,'' said Johannes Legner, spokesman for the government agency that oversees the so-called Stasi files in Berlin.

Legner said he expected pressure to grow on Washington to release the files now that his office has cracked the code on four bands of Stasi magnetic tapes.

German officials say the tapes have thus far revealed some 4,500 sources, but not necessarily agents, who provided information from 1969 to 1987.

The value of the information lies largely in that it reveals data about how East Germany's foreign spying worked, information that had been thought to be largely destroyed, Hans-Gert Lange, spokesman for the federal Office for the Protection of the Constitution, which is responsible for domestic intelligence surveillance in Germany.

The files held by the CIA reportedly identify foreign agents, but do not reveal what secrets they delivered. Der Spiegel newsmagazine this week said the newly decoded tapes could help fill in the blanks.

Legner said Wednesday that the new material is ``of such density, that it doesn't make sense in the long run to leave to speculation who the source was.''

But he added in many cases, the information on the tapes points to such a small circle of suspects that the spies could be unmasked even without the files in Washington.