In their second major air battle in three months, Israeli, warplanes, including U.S.-made F15 fighters, shot down four Mig 21 fighters of the Syrian Air Force south of Beirut today, Israeli officals reported.

Israeli Air Force sources said the air battle followed a series of "aggressive approaches" to Israeli reconnaisance aircraft recently, including an incident Wednesday in which Syrian Mig 23s fired missiles at an Israeli formation above Lebanon.

Israel said tonight that it intends to continue its reconnaissance flights over Lebanon to pinpoint Palestinian bases and monitor guerilla movements.

(In Washington, State Department spokesman Tom Reston called the dogfight a "dangerous development" and said Washington has been in contact with Jerusalem about the use of U.S.-made F15s.)

Israel also indicated it does not plan to suspend use of the sophisticated F15 fighter-bombers, which were sold to Israel in 1976 on the condition that they be used only for self-defense.

"If they (the Syrians) wouldn't intercept our flights in Lebanon, there wouldn't be any dogfights in Lebanon . . . We are going to continue according to the government policy," Maj. Gen. David Ivri, the Air Force commander, said in a briefing tonight.

On June 27, in the first air battle in the Middle East in five years, Israeli warplanes shot down five Syrian Mig 21s in air battles over the Lebanese cities of Tyre and Sidon, about 30 miles north of the Israeli border. The dogfight broke out as Israeli warplanes headed north to bomb and strafe suspected terrorist bases near Damour, just north of Tyre.

F15s also were used in those air battles, marking the first time that the radar-equipped aircraft ahd been used in aerial combat.

Ivri and Maj. Gen. Yoshua Saguy, chief of intelligence for the Israeli armed fordes, said a routine, weekly Israeli observation patrol of Israeli-made Kfir fighters, accompanied by a protective cover of F15s, was intercepted today by the Migs five to seven miles southeast of Beirut at an altitude of over 30,000 feet.

In an aerial battle lasting not more thatn 1 1/2 minutes, all four Syrian Migs in the formation were shot down by Sidewinder, Sparrow and Shafrin air-to-air missles and artillery fire, officials said.

Syria's offical Damascus Radio confirmed that four of its planes "were hit," but claimed that two Israeli planes were shot down. Israel said all of its planes returned safely to base.

(A Syrian spokesman said the Syrian planes had intercepted Israeli combat aircraft flying attacks on refugee camps south of Beirut, Reuter reported).

Ivri said Israeli pilots spotted three parachutes descending after the battle. Two of the Migs reportedly exploded in the air, and two more crashed to the ground.

Saguy said the Syrians in recent weeks have signaled a "constant intention to declare their policies in the skies of Lebanon," and that Israeli radar had spotted Syrian fighters about twice a day.

On Wednesday, officials confirmed today, the more advanced Mig 23s attached an Israeli reconnaissance patrol and fired air-to-air missles, scoring no hits. The Israeli aircraft withdrew.

Saguy said tonight that the Wednesday incident -- which Israeli officials refused to confirm last week -- and today's air battle appeared to be an attempt to divert attention from Syria's internal problems, specifically the opposition to the Moslem Alawite sect of President Hafez Assad.

Other Israeli sources speculated that the Syrian aggressiveness could be connected to Assad's upcoming visit to Beirut or that it might result from increased pressure by the Palestinian Liberation Organization.

When asked about U.S. State Department concern over the use of F15s over Lebanon, Ivri said, "We have to keep our observation of the area . . . We want to be sure we know everything going on in Lebanon . . . We will keep our observations, but we don't have any intentions of fighting Syrian Migs if they don't interfere with us."

Ivri said Israel used F15s in self-defense today, and that "everytime they (the Syrians) lose planes, they are getting replacements from Libya . . . We are going to continue according to government policy. If they (the government) are going to stop us, they are going to stop us."