Voting on President Reagan's judicial nominees, as Sen. Slade Gorton (R-Wash.) learned Thursday, has become risky political business.

Gorton's last-minute trade -- he voted in favor of appeals court nominee Daniel A. Manion in exchange for White House approval of Gorton's own U.S. District Court candidate in Seattle -- did more than keep the Manion nomination alive in the Senate. It gave his Democratic opponent in the November election, former transportation secretary Brock Adams, a ready-made issue that Adams wasted no time in seizing.

"Slade Gorton couldn't deliver without selling out his principles and everything he believes in," Adams said yesterday from Seattle. "I think it's tragic. A lifetime appointment to the Court of Appeals should be held to a different standard. It is going to be a big issue out here."

Gorton, however, decided that getting his man on the district court in his state was more important than a far-off appeals court vacancy in Chicago, spokesman David Endicott said. "The issue is whether or not Gorton stands up for the state of Washington," Endicott said. "He held out for our judicial candidate."

For years, judgeships were rubber-stamped by the Senate with few questions asked and scant public attention. But the increasingly partisan controversy over the quality of Reagan's nominees and his attempt to reshape the federal judiciary is becoming a nettlesome campaign issue for Gorton and other senators seeking reelection.

Sen. Arlen Specter (R-Pa.) has angered conservative Republicans by breaking with the administration to oppose the nominations of Manion and District Court nominee Jefferson Beauregard Sessions III of Alabama. At the same time, Specter's Democratic opponent, Rep. Bob Edgar (D-Pa.), has accused him of "political expediency" for later voting to send both nominations from the Judiciary Committee to the Senate floor with no recommendation.

Sen. Howell Heflin (D-Ala.), following a different path than Gorton, turned his back on a home-state candidate three weeks ago by casting the decisive vote to kill Sessions' nomination in committee. Heflin was lauded by civil rights groups, but a Mobile newspaper that backed Sessions labeled Heflin a "traitor."

"Senators' actions on judges are becoming a salient issue," said Ann Lewis, director of Americans for Democratic Action, which opposed the Manion nomination. "By moving this nomination like it's the latest public works appropriation -- by trading so openly and blatantly -- the administration has shattered its own claims that the judicial confirmation process is somehow above partisan politics."

Reagan administration strategists, however, say the Democrats are waging a blatantly ideological campaign to keep qualified conservatives off the bench. They say this assault will backfire in the face of strong public support for judges who share Reagan's philosophy.

For the time being, the confusing parliamentary maneuvers that produced a Senate deadlock on Manion's nomination have left the Republicans with a tactical advantage. Democratic opponents, who have criticized the former Indiana state senator as too inexperienced and too extreme for the 7th Circuit Court of Appeals, had planned on holding up the nomination with a filibuster.

On Thursday, however, thinking they had the votes to kill the nomination, they went ahead and allowed a roll call. "We had a two-vote cushion," a Democratic Senate aide said. "That's why we took the chance."

But the margin evaporated when Gorton switched sides and Sen. Nancy Landon Kassebaum (R-Kan.), after voting against Manion, withdrew her vote as time expired. The Republicans told Kassebaum to abstain to offset the absence of a Manion supporter, Sen. Barry Goldwater (R-Ariz.), but it turned out that Goldwater had made no commitment and purposely declined to vote.

This and other procedural moves by Majority Leader Robert J. Dole (R-Kan.) have sparked strong Democratic criticism. Dole agreed to a vote only after two Democratic senators promised to abstain to offset the votes of two GOP Manion supporters who were out of town. But one of the Republicans, Sen. Bob Packwood (R-Ore.), said yesterday he is undecided and that "Bob Dole never talked to me and he has no authority to do what he did." A spokesman for Dole said yesterday that he made no agreements involving Packwood precisely because he had not spoken with him, and that the Democrats acted on their own.

The tally was 47 to 47. With Vice President Bush in the chamber to break the tie, Minority Leader Robert C. Byrd (D-W.Va.) voted with Manion's supporters so that he would have standing to move for reconsideration of the vote, which he did. (Parliamentary rules say that only a senator voting on the prevailing side may move for reconsideration.) A move to table the motion for reconsideration will be pending when Congress returns after its July 4 recess.

While the Democrats may still have 49 or 50 votes against the nomination, they now face two procedural votes to wipe out the earlier result before they can get an up or down vote. They concede that wavering Republicans are more likely to vote with their party on a procedural matter, which would make Manion's confirmation final.

Moreover, Republicans who were willing to vote once against Manion -- such as Gorton's fellow senator, Daniel J. Evans (R-Wash.) -- may not be able to resist continuing White House pressure to back the president's nominee.

Evans had joined Gorton months ago in recommending William Dwyer, a Democrat with a liberal reputation, for a district court vacancy in Washington state. But like many other judicial candidates proposed by Republican senators, Dwyer's nomination was stalled at the Justice Department because of concern that he is not sufficiently conservative.

Gorton, a longtime acquaintance of Dwyer, was determined "to sandblast the nomination out of the Justice Department," spokesman Endicott said. At the same time, he said, Gorton had told senators that he would oppose Manion on grounds that the Indiana lawyer's qualifications were "no more than marginal."

Thirty seconds after the vote began Thursday, Gorton took a call in the Senate cloakroom from a senior White House official, who told him Dwyer's nomination would be approved if the senator voted for Manion. Gorton, a former state attorney general with a straight-laced reputation, agreed to switch sides.

Endicott defended the swap as "the way the Senate works," saying Gorton decided to accept Manion as the choice of Indiana Republican Sens. Dan Quayle and Richard G. Lugar, as long as he received the same "courtesy."

"We don't live in Indiana; we're not going to have to live with any modestly qualified decisions made there," Endicott said. "He's the person they want."

In Pennsylvania, Specter has won praise from blacks and civil rights activists for opposing Manion and Sessions. But conservative activists vowed to get even with Specter and tried to recruit Gov. Richard Thornburgh (R) to oppose him.

"It gets the conservatives mad, and they're already angry with him on a whole slew of votes," said Specter spokesman Dan McKenna. He said the votes demonstrate that Specter "is independent, he's his own man. People admire you to some extent because you do your own thing."

But Specter has also drawn criticism for voting in committee to report the nominations, saying that the full Senate should make the final decision. When Specter voted to reject Sessions but then joined an unsuccessful attempt to report the nomination without recommendation, Edgar accused him of "passing the buck."

"He wants to have it both ways, to appease Republicans one moment and then go to the civil rights groups and say 'I voted against him,' " said Edgar spokesman Ted Piccone. "It's spineless."

Sessions' defeat was even more sensitive for Sen. Jeremiah Denton (R-Ala.), who fought for the nomination to the end. Denton charged that there was "a political conspiracy" in Alabama to unfairly portray Sessions as insensitive to civil rights and thereby damage Denton's campaign against Rep. Richard C. Shelby (D-Ala.).

Sessions' nomination sparked controversy in part because, as the U.S. attorney in Mobile, he unsuccessfully prosecuted black civil rights activists in Alabama's rural "Black Belt" on voting fraud charges. Critics said this was an attempt to intimidate black voters who might turn out against Denton, a charge that both the senator and Sessions strongly denied