What was going on when I was born?

Israel said tonight that its air force destroyed the Syrian surface-to-air missile system in the Bekaa Valley of eastern Lebanon ''in a concentrated strike'' this afternoon. Twenty-two Syrian MIG's were reported shot down in the air battle that accompanied the raid, and seven more were said to have been hit. Israel said all its planes returned safely. It did not disclose the number of planes involved. (Syria said 90 Israeli planes attacked the SAM batteries. It said 19 Israeli and 16 Syrian planes were shot down.)

The Dow Jones industrial average sank to 795.57 yesterday, piercing the 800-point mark widely regarded as a key support level. The selling pressure reflected the combined pressures of the intensifying Middle East crisis, high interest rates, the weakening economy and the continued inability of Congress to reach a compromise on the budget deficit. The blue-chip barometer, which was off almost 10 points at 3 P.M., recovered somewhat in the last hour of trading on bargain hunting. At the close it was down 6.66 points. In the last four weeks the average has tumbled 74 points.

The Mobil Corporation announced yesterday that it would end its oil exploration and production operations in Libya by July 13. Mobil, the nation's second-largest oil company, did not explain why it was withdrawing from Libya beyond saying in a prepared statement that the decision was based solely on economics. Industry analysts said that Mobil might have been under pressure from Saudi Arabia to withdraw from Libya, because the two Arab nations are at odds. Mobil is one of the four American oil companies in the Arabian American Oil Company, which produces most of Saudi Arabia' oil. Mobil becomes the second to announce its withdrawal from Libya. The Exxon Corporation said last November that it was withdrawing from the North African nation, which as recently as 1980 was the third-largest source of American oil imports. A few days after Exxon announced its plan to withdraw, Mobil said that it had halted oil production in Libya.

Graduating seniors at Medgar Evers College in Brooklyn held their own commencement last night after the college president canceled it. The ceremony combined elements of black culture and Western academic tradition. The school's 11th annual commencement for the 418 seniors was held at the Brooklyn Academy of Music by a coalition of students, faculty members and community residents. After students marched in to the auditorium to a recording of the gospel song ''Peace Be Still'' and the poetry of Nikki Giovanni, a black poet, speaker after speaker recalled the recent protest at Medgar Evers surrounding complaints about its president, Dr. Richard D. Trent. They also called on the seniors to continue to fight for equality and freedom as they entered their chosen professions.

Tens of thousands of Americans apparently are illegally avoiding taxes on dividends, interest and other sources of income by having the funds sent to foreign addresses. The practice is costing the Government hundreds of millions of dollars in uncollected taxes, Internal Revenue Service audit documents indicate. Under current Federal tax law, income on dividends, corporate bonds residential and commercial rents and royalties sent to foreign addresses is generally subject to a 30 percent tax that the paying institution must withhold. But under treaties that the United States has with 50 countries, this tax is reduced to between 15 percent and nothing for legitimate residents of those countries.

Israeli and Syrian jets fought two large battles this afternoon over Syrian antiaircraft missile sites in eastern Lebanon, according to communiques made public here. A military spokesman reported that 19 Israeli fighter-bombers - F-15's and F-16's - had been shot down. He said the Syrians had lost 16 planes. A Damascus official said later that the missiles destroyed by the Israeli attacks had ''already been replaced.'' Late in the evening, a Syrian communique said that Israeli planes had bombed a village three miles west of Damascus. Eight civilians were killed and 47 wounded, the communique added. Israel denied carrying out such a raid.

Treasury Secretary Donald T. Regan, who has predicted sharp declines in interest rates in the past, cautioned today against expecting any dramatic decline in interest rates this year, even if Congress approves a budget resolution and then a budget. Turning to domestic matters after attending the economic summit conference at Versailles, France, last weekend, Mr. Regan said the prime rate should fall to 14 percent by the end of this year from the present level of 16 percent at a few banks and 16 1/2 percent generally. Beyond that, Mr. Regan was unsure what might happen to interest rates. ''Just how much further they might come down I don't know,'' he said in an interview. ''I don't know because you are battling psychology here,'' he added, referring to the fear of future deficits and skepticism about the permanence of the improvement in inflation. ''This is something - and I'm not trying to waffle on this - this is something that is outside the experience of all of us in interest rates.''

A power failure blacked out most of the south side of the 110-story office tower at 1 World Trade Center just after 2 P.M. yesterday. It stalled eight elevators carrying passengers for varying periods and interrupted five television stations' programs for about half an hour. One interruption was in Channel 13's telecast of Shakespeare's ''All's Well That Ends Well.''

Despite public antipathy and professional skepticism, the Reagan Administration is pressing its ambitious civil defense program. Page B20. By LESLIE BENNETTS The City Council yesterday rejected the Reagan Administration's proposal for the development of a plan to remove New York City residents to ''host'' areas upstate in the event of a nuclear attack. In a resolution adopted by a vote of 35 to 5, the Council rejected the Administration's plan to spend $4.2 billion over seven years on what is termed ''crisis relocation'' planning for urban areas around the United States. The proposal has yet to be approved by Congress.

A chart in Business Day on May 20 incorrectly stated the ratio of surplus to loss in the first quarter for United Mutual Savings Bank and the net operating income for Manhattan Savings Bank. The ratio for United Mutual was 3.3. Manhattan Savings lost $8.4 million in the first quarter.

Israel's ground forces drove to within sight of Beirut today as its fighter-bombers struck heavily at Syrian surface-to-air missile batteries east of here. An Israeli amphibious force established a bridgehead of five tanks and an undetermined number of infantrymen at Khalde, on the coastal highway four miles south of here near the Beirut International Airport. The bridgehead, which was spotted by reporters, came under machine-gun and mortar fire from Palestinians dug in on the beach and along the highway. (Israeli planes bombed Beirut's airport Thursday, and fierce battles between Israelis and Palestinians raged along the Lebanese coast south of the capital, according to a Reuters report that quoted the Government radio. The radio said an Israeli attempt to land at the airport had been repulsed.)

An article last Monday in Metropoli- tan Report about a law panel that views atomic arms as illegal incor- rectly identified John H. E. Fried. He is a former consultant to the United Nations on international law and a re- tired City University professor of political science.