They serve Uncle Sam but rarely vote

For three consecutive national elections, Eugene (Red) McDaniel had no chance to vote. He was a POW in North Vietnam, isolated for long periods and frequently tortured for communicating with other prisoners or trying to organize escape attempts.

Today, the retired United States Navy captain says he believes that of all people, men and women in uniform should participate in the democratic process. He is leading a bipartisan effort to encourage and help active-duty military personnel and their families register and vote. The results could have a significant political impact.

''For those in the military who serve and die to maintain this precious privilege, the right to vote should hold special meaning,'' says the tall, lean former aviator. ''And it is important that our military personnel be given every opportunity to exercise this right.''

Service people and their spouses vote even less regularly than the increasingly apathetic American public. By some estimates, only one-fourth of the 2.1 million men and women in the service are even registered.

This has to do with their frequent moves and overseas postings. Some 80 to 90 percent must vote by absentee ballot. Often such ballots, mailed back to hometown officials, arrive well after the election. The Rand Corporation found that up to $250,000 armed-forces personnel and their dependents were thus disenfranchised in 1980.

The American Defense Foundation, headed by Mr. McDaniel, is organizing veterans, military retirees, and other volunteers living near military bases to help register service men and women. The group also is lobbying the 34 states where late mailing of absentee ballots makes it difficult, if not impossible, to vote on time.

Recent elections have shown that sending out absentee ballots sooner can make a difference. Republicans took advantage of California's loosened regulations regarding such ballots, and rounded up absentee voters (many of them in the armed services). They say this was one key to helping George Deukmejian defeat his Democratic rival for the governorship.

The American Defense Foundation's effort is described as bipartisan, and the group does include three Democratic and five Republican lawmakers on its board of advisers. But there is a political cast to the organizing: The Democrats, as well as the Republicans, are strong supporters of the Pentagon. Two of them - Sen. Jeremiah Denton (R) of Alabama and Rep. John McCain (R) of Arizona - are also former POWs.

McDaniel's last job in uniform was as the Navy's envoy to the House of Representatives. Representative McCain finished his armed service career lobbying the Senate for the Navy. The recently formed 20,000-member group McDaniel heads does have a lobbying arm, and last year the President asked him to help twist arms on behalf of the MX.

The Republican Party has contributed to McDaniel's effort, but the Democrats have yet to. This may have to do with the perception that military personnel are more apt to be conservative and hence vote Republican, or at least tilt to the right of the Democratic Party line.

''I'm not going to disagree with that,'' said Paul Jensen, the foundation's legislative director.

The Defense Department itself has a big push to register voters in the military, and there is at least a secondary political motive here.

''Those who have volunteered to serve this great nation should be in the forefront in shaping and influencing its future through the electoral process,'' Defense Secretary Casper W. Weinberger wrote in a recent directive to military commanders.

Those in uniform (especially the officer corps) have traditionally been ''encouraged'' to be apolitical. But this is changing in the same way that Vietnam veterans are now more generally accepted in American society. Thus, any increase in voting or other political activism by the more than 2 million men and women in uniform (plus their families) could be a big plus for those advocating more defense spending and a setback for reformers trying to change such things as military retirement.

''The right to vote is a very private, personal thing,'' says McDaniel, a recent convert to the Republican Party who unsuccessfully challenged Rep. Charles Whitley (D) of North Carolina two years ago.

''But I don't hesitate to say I like President Reagan's defense policies. And I would encourage people to select the candidate who would perhaps support a strong defense policy.''