MANILA, SEPT. 19 -- Gunmen ambushed a top Philippine leftist leader tonight, killing him less than an hour after he had publicly called for huge street protests Monday against what he said is growing military influence in President Corazon Aquino's 18-month-old government.

Leandro Alejandro, 27, was killed instantly and his driver and two colleagues were seriously wounded when gunmen inside a van blocked their car and opened fire with automatic weapons just a few feet away from the suburban Quezon City headquarters of Alejandro's left-wing coalition, Bayan.

The slaying, the latest in wave of gangland-style murders that included last month's assassination of one of Aquino's top Cabinet aides, touched off speculation by radio commentators and political activists that it would result in the declaration of a national state of emergency.

The killing deepened the political crisis that has plagued Aquino since an Aug. 28 military uprising paralyzed her government and polarized the military.

Military authorities, who 10 days ago had announced plans to arrest Alejandro during one of his many street protests in Manila, said they had no clues to the identity of his killers. They speculated that it was the work of a right-wing civilian death squad.

Leftist leaders, however, immediately blamed the Aquino government, and Alejandro's widow, Lydia, said she holds the 54-year-old president responsible.

Alejandro's organization also sought to link the killing to the recent attempted coup by renegade military officers under Col. Gregorio Honasan, who is now a fugitive. Honasan was one of the leaders of the successful 1986 revolt against president Ferdinand Marcos that brought Aquino to power.

Aquino's press secretary, Teodoro Benigno, read a government statement calling the killing "a very tragic travesty of law and order, specially at a time when President Aquino is calling upon everyone to join hands."

Alejandro angered the Aquino family in May when he ran for Congress against Aquino's sister-in-law, Tessie Aquino Oreta, who had publicly labeled Alejandro, a former student activist, a Communist.

Shortly before he was killed, Alejandro held a news conference to announce Monday's planned street protests against "rising militarism" in the aftermath of the Aug. 28 uprising.