The Republican presidential candidates for 1988 will have a hard act to follow, according to a Washington Post-ABC News poll that takes an early look at what the public thinks of the people who are now widely considered the main contenders.

Only one of the GOP's prospective 1988 candidates, Vice President Bush, comes close to President Reagan in making a favorable impression on the public. Two others, Senate Majority Leader Robert J. Dole (R-Kan.), and the man who held that position before Dole, former senator Howard H. Baker Jr. (R-Tenn.), have lower name recognition and could end up siphoning each other's support, the poll suggests.

The fourth likely candidate, Rep. Jack Kemp (R-N.Y.), is at the bottom in name recognition but seems to be having moderate success in staking himself out as the conservative alternative to Bush.

As for Reagan, the survey of 1,506 people, conducted July 25 to July 29, shows him making a more favorable impression than any of 11 other leading Republicans or Democrats tested. His overall rating is 65 percent favorable, 31 percent unfavorable. The favorability rating is not far from the highest Reagan has received during his presidency and may be linked in part to sympathy for the president after his cancer surgery.

The survey also asked people about former president Richard M. Nixon. Only 28 percent of respondents gave him a favorable rating -- a score not much higher than his approval rating when he resigned in August 1974.

Following are thumbnail sketches of how people across the country see these Republicans: George Bush

Bush has far higher name recognition and favorable ratings than any of the other leading potential candidates. His overall score among all people -- Republicans, Democrats and independents -- is 59 percent favorable, 28 percent unfavorable. That is better than any Democrat tested, and second only to Reagan among Republicans. Among strong Republicans, the people who often decide low-turnout presidential primaries, Bush scores 87 percent favorable, 5 percent unfavorable.

*Strengths: Bush makes a positive impression at this stage on a majority of people in all age groups, all regions, and among liberals as well as political moderates and conservatives. He has a substantial head start.

*Weaknesses: Bush's public image is that of someone standing in Reagan's shadow: If people like Reagan, they also like Bush; if they do not like Reagan, they dislike Bush. Thus, his high ratings could fall when Reagan steps away and the other candidates home in on Bush. Additionally, Bush gets only a mediocre 44 percent favorable, 44 percent unfavorable rating from self-described Democrats, a more negative score than his opponents received, even with their lack of name recognition. Robert J. Dole

Despite his prominence as Senate majority leader and a former vice-presidential candidate, 49 percent of the people interviewed do not know Dole well enough to rate him. Those who do rate him, however, give him a solid 36 percent favorable, 15 percent unfavorable score.

*Strengths: If Dole's name recognition is not high, it is nevertheless substantially above what it was in his last presidential bid, in 1980, and his Senate position allows him to stay in the public eye. Among those who rate him, he scores better than 2-to-1 positive in every region and most age groups and among moderates and conservatives.

*Weaknesses: He does much worse than Bush and trails Baker slightly among the key "strong Republican" group, who score him 53 percent favorable, 14 percent unfavorable. So far as the public is concerned, he and Baker appear to be look-alikes, "responsible Republicans" not tied to Reagan, fighting for the same constituency. Howard H. Baker Jr.

Like Dole, he gets good ratings from those who have an impression of him. But 46 percent have no strong opinion of him. His overall figure is 38 percent favorable, 15 percent unfavorable. Among strong Republicans, it is 59 percent favorable, 11 percent unfavorable.

*Strengths: A Tennessean, Baker does best in the South, where his 45 percent positive, 14 percent negative rating is slightly better than that of the other candidates. He also places first among liberals, slightly ahead of Dole, and, because of his southern support, gets a 36-20 favorable score among Democrats, the best of any Republican.

*Weaknesses: They are the same as Dole's. Both will have to accentuate differences between themselves even as they take on Bush, or they will see their support diluted. Jack Kemp

Some say the New York congressman is running harder than all his opponents combined, but that may be out of necessity: Hardly three people in 10 know enough about Kemp to have an impression of him. Among that small group, 21 percent see him favorably, 10 percent unfavorably, a 2-to-1 ratio that is in line with those of the other likely candidates. Among strong Republicans, Kemp's score is 33 percent favorable, 9 percent unfavorable.

*Strengths: Kemp's appeal is that of a more conservative Republican: He does best among those in the top one-third on the Post-ABC News poll's socioeconomic scale, drawing a 29 percent favorable, 13 percent unfavorable rating. With people who see themselves as conservatives (including Democrats), his score is 26 percent favorable, 9 percent unfavorable.

*Weaknesses: Kemp runs the risk of catering to too narrow a constituency. At the low end of the socioeconomic scale, his rating of 12 percent positive, 11 percent negative is much worse than Baker's and Dole's and somewhat worse than Bush's. Richard M. Nixon

Nixon's overall rating is 28 percent favorable, 64 percent unfavorable. By contrast, his last presidential approval rating in a Gallup poll, in August 1974, the month he resigned, was 24 percent positive, 66 percent negative.

In no group does a majority or plurality look on him favorably. The best he does is among strong Republicans, where 47 percent give him a positive rating and 47 percent a negative one. Among all Republicans and Republican leaners, he scores 37 percent favorable, 56 percent unfavorable. By region, he scores 20 percent favorable in the West, 29 percent in the East and Midwest, and 32 percent in the South.