Whatever its impact on the Democratic Party, Sen. Edward Kennedy's semi-candidacy scrambles the contest for the Republican nomination. It puts a cloud over Ronald Reagan. It boosts the chances of Howard Baker and John Connally. It opens the race to still other possibilities.

Up to now Reagan has seemed to have everything going for him. He has name recognition and organization and a strategy that diminishes his most vulnerable point -- a reputation as a far-out conservative.

Most important of all, the polls have shown him whipping Jimmy Carter. Since winning is the name of the game, topping the president tended to solidify Reagan's position. He was not only the man Republicans liked best in their hearts. He didn't trouble their heads. There was no pressing reason to go against him.

But matched against Kennedy, Reagan runs second. The prospect of losing with Reagan inevitably raises questions in the minds of Republican workers and voters -- questions about his age, about his effectiveness as a leader and about his capacity to win the moderate, middle-of-the-road vote. So Reagan now has a dimmed chance for winning the nomination on the strength of sheer momentum.

To be sure, Kennedy tops all other Republicans in the polls. Robert Teeter, the astute Michigan pollster who worked with the last two Republican presidents, says that when the prospect of a Kennedy campaign is mentioned, "many Republicans act as though they just heard there was a tidal wave offshore. They run for cover."

If so, Reagan might still get the nomination by default. Like Barry Goldwater in 1964, he would be anointed as a nice buy who served the party well and could easily be sacrificed in a losing cause.

But the prospect of a civil war in the Democratic Party works to break up the "tidal wave" outlook. Especially since a couple of Republican candidates are apt to do far better against Kennedy than Reagan.

Baker, the minority leader from Tennessee, is one. Now he generally trails Reagan in the polls of Republicans by about 2 to 1 -- or 45 percent to 22 percent. Despite a lack of organization, despite the press of duties in the Senate and despite difficulties in launching a campaign, Baker has been steadily gaining strength.

The reason is that Baker has few evident weaknesses. He is not only intelligent and experienced and good on television. He is a genuine moderate. So he is a natural rallying point for opposition to a front-runner.

That asset grows of Kennedy becomes the candidate. The vast number of voters who are anti-Kennedy, for one reason or another, will not find insuperable barriers in the way of going with Baker. On the contrary, as a man from the Border, he is particularly well-placed to attract the Southern and Midwestern voters most apt to harbor anti-Kennedy feelings.

As to Connally, while impressive to businessmen and many persons in the press and television, he has so far not been able to win the affection of Republican voters. The polls show him with consistently half of the Baker vote -- about 10 percent. But a Kennedy candidacy could achieve one thing Connally has not been able to achieve for himself -- a launching.

Connally alone has the personal magnetism to contend with Kennedy's star qualities. He is strongest with precisely the voters most prone to hate Kennedy -- the conservative Southern Democrats. Moreover, his biggest weakness -- Watergate and the wheeler-dealer image -- tends to be offset by Chappaquiddick. As one Connally organization man put it: "A Kennedy candidacy wipes out the honesty dimension."

The mere possibility that Reagan can be stopped inevitably raises the hopes of all other Republicans in the race. People talk of Gen. Alexander Haig even though he has Veitnam on his hands, and Watergate. Even that darkest of dark horses -- John Anderson, the fine congressman from Illinois who has truly impressive moral and intellectual qualities -- now has a chance.

A far more likely prospect is for a reentry on the board by Gerald Ford. The former president has been telling friends that if Reagan won the New Hampshire primary by more than 35 percent of the vote, he would have the nomination. But Ford has also been saying that if Reagan's margin were smaller, the whole Republican race would have to be reassessed.