Rep. John H. Buchanan, a Baptist minister and for 16 years a Republican member of Congress, fell victim to the Rev. Jerry Falwell's Moral Majority Tuesday and was defeated in his bid for reelection.

Buchanan, who had survived tough primary fights in previous years, lost to ultra-conservative Albert Lee Smith by 55 percent to 45 percent.

Buchanan's moderate-conservative voting record had made him enormously popular in the Birmingham district he represented since 1964, but his moderate stands in support of blacks and women offended the conservatives in his party.

In past primaries, he had depended on Democratic crossover votes to defeat his conservative challengers, but on Tuesday more Democrats crossed over to support Smith than Buchanan.

Many moderate Democrats apparently stayed in their own party to vote in the Senate prmary for incumbent Sen. Donald Stewart. Meanwhile, Smith attracted conservative Democratic voters.

Buchanan was elected to Congress along with four other Republicans from alabama in 1964, when Sen. Barry M. Goldwater of Arizona was the GOP presidential nominee. Buchanan was a member of the Education and Labor and Foreign Relations committees, and often voted in support of the Carter administration.

Alabama's 6th Congressional District is a curious combination of suburban rich and city black. Although the black vote is about 40 percent of Birmingham, it is less than a third of the whole district.

Smith ran unsuccessfully two years ago, but this year he had the active support of Falwell followers. "The difference is we had 2,500 volunteers this time, and last time we had 1,000," Smith said Tuesday night, saying that he was stunned by his victory.

The Rev. Richard Vigneuelle said his Birmingham Moral Majority organization did not specifically endorse Smith by name. "We went out to educate the people on moral issues," he said of his door-to-door effort, "but we didn't support a particular candidate."

Smith, once active in the John Birch Society, was also aided by other right-leaning groups.

What the 2,500 newcomers did was turn a safe Republican seat into a tossup in November, Smith's opponent, Democrat Pete Clifford, a stocky talkative city councilman, has occupied the right wing of his own party, where it is popular to oppose the ERA and similar liberal causes.

As a council member, he has never before needed to consider Birmingham's black vote. A serious race will require the support of Mayor Richard Arrington, but the city's canny new black mayor is sure to exact some Buchanan-like stands on women and blacks.

Clifford was unopposed as his party's nominee because Buchanan was considered unbeatable in the November election. The morning after the Republican bloodletting, however, politics looked altogether different.

As one insider put it, "there are Democrats all over the place kicking themselves for not being this year's sacrificial lamb."