Residents of Somerset last week overwhelmingly voted their support for an immediate freeze on both Soviet and U.S. nuclear weapons and a subsequent reduction in atomic arms.

In a special election, the residents approved by a 269-to-48 vote a referendum calling for a "bilateral, verifiable freeze on the testing, production and deployment of nuclear weapons." The vote came a week after a Defense Department official and a Somerset scientist debated the issue at a local meeting.

The Town Council asked Mayor A. Eugene Miller to notify the president, secretary of state and members of the House and Senate foreign relations committees of the referendum results, Town Clerk Marty Kline said. Miller is expected to deliver the letters this week.

Half of the town's 685 registered voters turned out for the special election. Twenty-six did not vote on the nuclear weapons proposal, Miller said.

"For the fact that we just had a major contested election and this is five or six weeks later, this is a fantastic turnout," Miller said.

Voters also elected Rowland E. Roberts to fill the council seat vacated when Miller was elected mayor May 3. Roberts garnered 160 votes, defeating Roberta Rovner-Pieczenik, who got 119, and Sue Rosenthal, who received 57.

The residents also approved a $396,334 town budget for next year, raising their property tax rate by 2 cents to 56 cents per $100 of assessed property value.

A week before the election, nearly 100 residents heard Ronald Lehman, a high-level Pentagon adviser on nuclear-forces policy, and Jeremy Stone, a Somerset resident and head of the American Federation of Scientists, debate the Reagan administration's arms policies and the current nationwide arms-freeze movement.

Lehman told the audience that a promise by the United States not to be the first to use nuclear weapons "would only satisfy those . . . who actually would believe we wouldn't use the first-strike capability."

He said the threat that the United States might fire nuclear weapons in response to a Soviet invasion of an allied European nation assures that Russian troops will never attempt an assault with "conventional forces."

Stone dismissed the Reagan administration's Strategic Arms Reduction Talks (START) as "not a serious proposal." He said he would favor an arms-limitation agreement similar to SALT II, but with the weapons ceilings 50 percent lower than called for in that proposal.