The crisis in Lebanon has brought a surge in Israeli Premier Menachem Begin's popularity five weeks before general elections. An opinion poll conducted last week when Israel and Syria seemed close to war said his Likud bloc was running neck-and-neck with the Labor opposition. It gave Likud and Labor 43 seats each in the 120-member Knesset. It also said 38 percent now thought Mr. Begin best suited to be prime minister, against 28 percent a month earlier. The Labor opposition, which until recently had been expecting a landslide victory, slipped in the poll. Party leader Shimon Peres was b acked by only 25.5 percent.