One of the police officers lost a foot in the blast, said Adil Surat, head of the trauma unit at Hacettepe University hospital, speaking to the Anatolia news agency.
A second officer was seen with scratches on his face and appeared to be in shock. His blue uniform was stained with the blood and flesh of his injured colleague.
Surat said the second police officer and an injured civilian, who were also evacuated to the hospital, were in good condition.
Ankara police chief Ercument Yilmaz said the police officers were injured when they approached a package containing the explosives to verify an anonymous tip that a bomb had been placed nearby.
The bomb exploded some 75 yards from the entrance of the hotel, shattering windows of nearby buildings.
Bush is scheduled to arrive in Ankara late Saturday night and is to meet Prime Minister Recep Tayyip Erdogan and President Sezer on Sunday.
Bush is visiting Ankara ahead of Monday's NATO summit in Istanbul that British Prime Minister Tony Blair, French President Jacques Chirac and other alliance leaders are also scheduled to attend.
Deputy Prime Minister Mehmet Ali Sahin said security measures would be heightened after the blast. Turkish media had been reporting that 7,000 police officers would be on duty in the capital for the Bush visit.
"Measures will be increased from now on," Sahin said. "There are people with bad intentions who can take every risk to fulfill their goal."
Taxi driver Mithat Aksoy was near the package when it exploded.
"I heard an explosion and thought lightning had hit," Aksoy said.
"Then I saw smoke at the area. ... I saw that an injured police officer was there," he said.
Several ambulances rushed to the scene.
Police sealed off the street and towed away vehicles parked there as a security precaution.
Militant Islamic, Kurdish and leftist groups have carried out past attacks in Turkey, and scores of people believed to be linked to such groups have been detained in security sweeps in recent weeks.
Concerns about security have grown in Turkey since last November, when four suicide truck bombings killed more than 60 people in attacks on two synagogues, the British consulate and a London-based bank. Prosecutors say a Turkish al Qaeda-linked cell carried out those attacks.
About a half-dozen small sound bombs explosives designed primarily to make noise and not cause serious damage have exploded in Istanbul in recent days. Leftist groups have used the bombs in the past. Several people have been injured, most by shattered glass.
Security in Istanbul is expected to be extremely tight for the NATO summit.
Turkish security forces are using concrete barriers to seal off a zone in the heart of the city and surveillance aircraft are being prepared to help monitor a no-fly zone over the area.
The Bosporus will also be closed to oil traffic ahead of the summit.