George Bush is the number one choice among delegates to the republican National Convention as a running mate for Ronald Reagan, according to a new Washington Post poll.

Bush places substantially ahead of Rep. Jack Kemp (R-N.Y.), who is second, and Sen. Howard H. Baker Jr. (R-Tenn.), who is a distant third.

But Bush, with 34 percent, falls far short of gaining majority support from delegates, and the poll suggests that the gathering that will convene in Detroit July 14 is prepared to give Reagan a lot of latitude in filling out the ticket.

Reagan is being tugged in opposite directions. On the one hand, some political observers feel it is important for him to choose someone who is perceived as a moderate, such as Baker, if he is to expand his base and win in November.

On the other, some longtime conservative Reagan backers are urging the former California governor to select a clearly identified conservative, such as Kemp. Many feel the choice is the most critical one that Reagan will have to make between now and the election.

In The Post's poll, Bush appeared to be the only prospective vice-presidential candidate with any broad appeal to both conservatives and moderates, with the majority that is going to Detroit committed to Reagan, and with the minority who had backed other candidates or who are uncommitted.

In contrast Kemp runs strongly among the one-fifth of the delegates who consider themselves "very conservative" politically, but gets hardly any support elsewhere. He has picked as Reagan's running mate by 21 percent of the delegates.

Baker got minimal support across the board, ending up as the first choice of only 9 percent of the 602 delegates interviewed. One apparent reason for Baker's poor showing, and for Bush's strong one, is the fact that Baker dropped out of the presidential race early, garnering only eight delegates, while 70 of the people polled by The Post are Bush delegates.

Baker picked up considerably when delegates were asked to name their second choice for vice president. But he still ran third, with 27 percent of the delegates mentioning him as first or second, compared to 47 percent for Bush and 33 percent for Kemp.

Perhaps Bush's strongest suit in The Post poll is a strong showing in sections of the country where Reagan needs assistance. Reagan is perceived as a powerful candidate in the West and South, weaker in the Northeast and Midwest.

Among the delegates, Bush does poorest as a vice presidential candidate in the South and West, but far stronger than anyone else in the Northeast, where he is supported by 55 percent of the delegates, and in the Midwest, where he is supported by 39 percent.

While Reagan will not be able to satisfy all his backers in his choice of a running mate, the poll strongly suggests that whatever he does will be greeted by cheers from the convention delegation. Many delegates told The Post they either had no vice presidential preference or that they were satisfied to leave the choice to Reagan.

Furthermore, in contrast to 1976, this Republican convention appears unified. Only eight delegates interviewed said they would not work for a Reagan victory in November; more than 90 percent said they would work hard for him.

The Post's poll was conducted June 24 to July 1, with a random sample of almost one-third of the convention's delegates selected for interviews by telephone on a variety of issues.

More than 90 percent of those selected were interviewed. Their make-up varied by no more than 1 percent in key characteristics from the actual makeup of the entire convention, strongly suggesting that the poll's findings represent the views of all delegates and not simply those interviewed. f

Also mentioned by delegates as preferred choices for vice president were Rep. Philip Crane (R-Ill.) and Sen. Richard Lugar (R-Ind.), both with 4 percent.

Former president Gerald Ford, who has said he is not interested in being on the ticket as the vice presidential running mate, got 3 percent.

The Post's poll coincides with a new Gallup poll testing voter attitudes toward a running mate for Reagan. That poll shows Ford as the favorite among independents and rank-and-file Republicans.

With Ford left out, Bush placed first, drawing 29 percent among both independents and Republicans. Baker was second, getting 15 percent from Republicans and 16 percent from independents.Placing third was former Texas governor John B. Connally, with 12 percent among Republicans and 9 percent among independents.