In a failed attempt to kill Prime Minister John Major and his war Cabinet, suspected Irish Republican Army terrorists fired three mortar rounds Thursday at his official residence at No. 10 Downing St., a government official said.

At least three people were slightly wounded in the daring daylight attack in central London that police said had all the hallmarks of an IRA strike. Three mortar rounds were fired, one of which exploded in a garden behind Downing Street, shattering windows and scorching a wall, police said."This reckless attack appears to be the work of the provisional IRA," Home Secretary Kenneth Baker told the House of Commons. He said it was an attempt to kill Major and Cabinet members meeting with him to discuss the Persian Gulf war.

There was no apparent link between the attack and Britain's involvement in the gulf conflict, Baker said.

Despite stepped-up security since the start of the gulf crisis, the terrorists were able to launch three mortar rounds from a white Ford van on Whitehall Street about 200 yards from No. 10 Downing St., the prime minister's home and office, police said.

One round landed about 45 feet behind No. 10 in a garden and two others struck the Foreign Office lawn, one of which detonated.

Three people, including two police officers on the diplomatic security squad, were hospitalized for slight wounds, said Scotland Yard spokesman Stewart Goodwin. The officers received cuts and bruises while a passer-by suffered a twisted ankle, he said.

The white van exploded after the mortars were fired, but it was not known if anyone was inside. Goodwin said the van had been left next to a statue of Lord Mountbatten, who was killed by an IRA bomb in 1979.

"It was driven to the junction and abandoned," he said, adding that only seconds elapsed between the time it stopped and the mortars were fired. He said police were investigating reports that two people were seen running away moments before the attacks began.

Smoke from the burning van billowed up and mixed with snow falling in Britain's worst winter storm in four years. The entire Whitehall area, the government office district, was sealed off and police searched for other unexploded devices.

After the blast, Major said, "I think we'd better start again somewhere else," according to a Downing Street spokeswoman. The meeting was adjourned briefly but resumed shortly in a more secure room.