A bomb explosion near the first Israeli Army checkpoint south of Beirut narrowly missed a passing Israeli military convoy today but injured six Lebanese waiting in the eight lanes of traffic for their credentials to be checked.

The attack was at least the fifth against an Israeli military position during the past 36 hours in an escalation of a clandestine guerrilla campaign, for which the Palestine Liberation Organization and leftist allies claim responsibility.

In the stalemate with Syria and the PLO over withdrawal of troops from Lebanon, Israeli troops are facing what resembles a war of attrition and taking the heavier casualties.

In Israel, the attacks are raising the level of impatience with the occupation in Lebanon, increasing the pressure on the government of Prime Minister Menachem Begin to take some action. There appears to be pressure to wage war against Syria and the PLO, but, at the same time, the majority does not appear to favor a unilateral pullback of forces.

Three Israeli soldiers were killed yesterday by guerrillas northeast of Tyre--the second fatal ambush this week. This raised the Israeli toll since Sept. 25, when last summer's war ended, to 114 killed and 235 injured. Estimates are that 495 Israeli soldiers have been killed since the invasion began last June.

Later yesterday, the Palestinian news agency Wafa and the Phalangist Christian Voice of Lebanon radio reported another attack on Israeli armored vehicles in southern Lebanon. There were no reports of injuries. Israel denied the reports.

Last night, guerrillas fired submachine guns at an Israeli Army checkpoint at the northern entrance of Sidon and later exploded a bomb near the Israeli military governor's quarters in Sidon as an armored convoy passed. There were no injuries either time.

The roadside explosion south of here today also appeared to be aimed at an Israeli convoy. An Israeli jeep, armored personnel carrier and water tanker had just passed the spot. At least six Lebanese in the pile of traffic lined up behind an Israeli checkpoint were injured, including a middle-aged man and his three children.