A years-long effort to supplant the Electoral College with direct popular election of presidents, with each vote carrying equal weight, met resounding defeat in the Senate yesterday.

Supporters of the constitutional amendment, led by Sen. Birch Bayh (D-Ind.), could muster only a 51-to-48 vote on the final roll call -- 15 short of the 66 they needed.

Although the Senate debate over direct election has gone on since 1966 under Bayh's guiding hand -- he has held 47 days of hearings on the issue -- it was clearly an issue that never caught on.

Sen. Strom Thurmond (R-S.C.), who carried the ball for the opposition, said after the roll call that his forces picked up a dozen votes since Sunday "because we did a world of work on this thing."

"We thought we had it won two days ago, when we dropped our opposition to the cloture vote," Thurmond said.

The debate-ending cloture vote, sought by Bayh, originally had been scheduled for yesterday, with the Indiana senator figuring he had a good chance of winning.

But wehn Thurmond and others agreed to shut down debate Monday, going straight to yesterday's final vote on the amendment, the handwriting was on the wall.

Distilled through weeks of off-again, on-again floor debate, the direct election issue came out this way:

Thurmond and his allies contended that no compelling case had been made for abolishing the Electoral College and that direct election was "radical" tampering with the Constitution.

"A dramatic adventure into the electoral unknown," was how Sen. Alan K. Simpson (R-Wyo.), described it. "One of the most important constitutional debates of our time," said Sen. Orrin G. Hatch (r-Utah), another opposition leader.

"The question is whether we are going to retain federalism or not. It boils down to that," Thurmond told the Senate just before the final vote.

Bayh and his forces, however, contended that the direct election of presidents and vice presidents, as the amendment proposed, would allow every voter's ballot to count equally in the national election.

"It stands for one thing -- that every vote will be treatedd equally. That is what it is about," said Sen. David Pryor (D-Ark.).

Bayh said the Electoral College system, which gives all of a state's elecoral votes to the candidate who wins the most ballots in that state, is a form of "American roulette" that threatens to undermine the polical system.

Bayh yesterday told a nearly empty Senate chamber that he had listened in "amazement" to the argument that direct election would lead to more voter discontent.

"Discenchantment of the people with our institutions and political leaders is one of our biggest problems today," Bayh said.

Direct election, he said, could stimulate interest in elections, be an incentive to state party workers to work for every vote and show clearly that an elected president "is at least the choice of most of the people of this country."

He suggested that direct election also could bring new trust in politicians. "Every poll tells use the people don't trust their political leaders. . . . They have less faith in their senators than in their garbage collectors," he said.

In a post-mortem, Bayh said yesterday's vote was heavily influenced by pressure from the Urban League and The American Jewish Congress on "progressive and liberal" senators upon whom he had relied for support.

Both organizations, in opposing direct election, had argued that the Electoral College now tends to give power to black and Jewish voters in populous states that might be diminised in direct elections.

Yesterday's floor vote on the amendment -- the first since Bayh began pushing it from his Judiciary subcommitee in 1966 -- brought together an unusual mix of conservatives, liberals, big-state and small-state senators.

Thurmond claimed to have picked up support in the final days from such diverse figures as Thomas F. Eagleton (D-Mo.), Paul S. Sarbanes (D-Md.), Russell B. Long (D-La.), Bill Brandley (D-N.J.) and Charles H. Percy (R-Ill.).

Early reaction to yesterday's vote, which virtually kills the issue in this Congress, came from Ruth J. Hinerfeld, president of the League of Women Voters of the United States.

Hinerfeld called the vote "a major blow for direct democracy in presidential elections. It holds this nation back from the 20th century." CAPTION: Picture, SEN. BIRCH BAYH . . . loses battle he began in 1966.