The only three senators to vote against sweeping anti-drug legislation warned colleagues they may feel "ashamed" of the bill once all the election-year fervor to crack down on drugs has passed.

But most senators rejoiced in the approval Friday of a measure that takes aim at both dope peddlers and casual users, creating a federal death penalty for drug kingpins and big fines for possession of even small amounts of narcotics."At long last we have put the burden of responsibility on the user as well as the pusher," declared Senate Republican leader Robert Dole of Kansas. "For too long, we have treated the buyer and user of illegal drugs as a victim."

Before adopting the broad legislation, the Senate easily approved "get-tough" provisions Friday denying most federal benefits to drug convicts and hitting casual users with fines as high as $10,000 for possession.

Overall, the $2.6 billion package increases spending for drug enforcement, interdiction, treatment and prevention but shifts the emphasis in fiscal 1990 to the latter side of the problem, consumer demand.

Retiring Sen. Daniel Evans, R-Wash., who joined only two others in opposing the bill, accused colleagues of piling on questionable amendments to the basic measure in fear of being labeled "soft" on drugs in an election year.

"I hope that in our rush to a drug bill," Evans said, "we do not end up going so far overboard that we will look back a year or two, or five years from now, and instead of being proud of what we've done be ashamed of what we've done."

The others who stood fast in voting against the bill were Sens. Mark Hatfield, R-Ore., and William Proxmire, D-Wis., who also is retiring.

Negotiators still must work out differences between the Senate version and an earlier House-passed measure before a final bill can go to the White House for President Reagan's expected signature.

The $2.1 billion House bill, considered an "assault on the Constitution" by critics, had been seen as even tougher than the Senate version until senators added most of the same provisions to their legislation.