Why the House turned down the MX missile

* ''The missile's credibility has been stretched by 'defense experts' who first wanted the race track and then dense pack,'' says Rep. Gene -Snyder (R) of Kentucky.

* ''This missile is inherently wrong when people are starving,'' says Rep. Gus Savage (D) of Illinois.

Those two reasons - the basing mode and spending priorities - were the keys to the defeat by the US House of Representatives of a $988 million bill to begin producing the MX missile.

The Monitor surveyed 145 congressmen who voted against the missile in an effort to find the underlying reasons for the defeat. During the vote on Dec. 7, a majority of the House supported an amendment by US Rep. Joseph Addabbo (D) of New York to withhold production money.

That vote proved to be the first tug that has pulled the rug from under President Reagan's plans to deploy the weapon. The House amendment has since served as the basis for a House-Senate compromise that eliminates production money for the MX and sets aside $2.5 billion for research and development, to be spent once Congress approves a basing mode.

The Monitor conducted its phone survey during the week following the House vote. Some 110 Democrats (76 percent) and 35 Republicans (24 percent) who voted for the Addabbo amendment responded. This approximates the breakdown in the total number of Democrats and Republicans who voted against the missile - 245, of which 195 (80 percent) were Democrats and 50 (20 percent) were Republicans. Some respondents didn't answer every question; others answered only parts of questions. Still, the survey gives a sense of why the House refused to underwrite MX production.

Participants were first asked to rank in order of importance eight possible reasons for their vote. Many didn't rank every answer, and some gave more than one answer equal ranking.

Of all reasons ranked as No. 1, ''The 'dense pack' basing mode won't work'' garnered 40.8 percent of the responses. Under the dense pack concept, 100 MX missiles would be placed in hardened silos packed into a 1.5-mile-by-14-mile rectangle near Cheyenne, Wyo. When the first incoming warhead explodes over the missile field, so the theory goes, it will either detonate other incoming warheads (fratricide) or knock them off course. This would leave the majority of MX missiles unscathed and ready for a retaliatory strike.

''Other,'' the second most popular answer under Ranking 1, received 17.8 percent of the responses. It allowed House members to list their own reason if their views weren't represented by the answers provided. Many of the comments under ''other'' also referred to the basing mode. For example, US Rep. Joseph D. Early (D) of Massachusetts noted that the dense pack is an unproven theory than is ''untestable without war.''

GOP colleague Vin Weber of Minnesota said he was very skeptical about dense pack and that Congress would be ''spending too much money on an uncertain basing mode.

His answer also touches on the third most popular response under the No. 1 ranking - ''The missile is too expensive,'' accounting for 14.6 percent of the answers. If a related answer, ''The military budget needs to be cut,'' is included, the budget aspect of the MX program becomes the second most popular No. 1 response, at 21 percent.

When participants were asked to rank the second most important reason for their vote, the top choices were the missile's expense (26.4 percent), the basing mode (21.7 percent), and the need to cut military spending (18.6 percent). Of the reasons ranked third in importance, the top three answers mirrored those under the second ranking, though the percentages vary.

Typical of the concern over spending was that of US Rep. Robert Garcia (D) of New York, who said the missile was ''one more instance of the administration trying to increase military spending at the expense of social programs.''

When the reasons for voting for the amendment are rated by the number of times they were selected - regardless of ranking - the basing mode is the most popular answer. The missile's expense is second and the military budget is third. If the two answers related to spending are combined, concern over spending becomes the most cited reason, with basing second.

The participants were asked to assess the impact of the vote on strategic arms reduction talks in Geneva between the US and the Soviet Union. Some 70.8 percent said the vote would have ''no impact'' on the talks, 24.2 percent had no answer, 16.7 percent said the vote would ''strengthen the US negotiating position,'' and 5 percent said the vote would ''weaken the US negotiating position.''

The final question: ''Should the MX missile be built under any basing mode?'' Some 47.2 percent said ''No'' (Broken down by party, a plurality of each also said ''No''); 18.1 percent said ''yes;'' 13.9 percent said ''perhaps;'' 13.2 percent didn't reply to the question; and 7.6 percent said they'd back more research and development.