HOUSTON, JULY 2 -- In their first debate, seven Democratic presidential candidates talked about trade, taxes and deficits. But the chances that any one of them will make it to the White House in 1989 could have as much to do with a question not asked: Should U.S. Appeals Court Judge Robert H. Bork be confirmed to serve on the Supreme Court?

As the candidates broke camp here today after Wednesday night's two-hour televised debate, the coming confirmation battle emerged as the kind of fight that could reshape the issue agenda of the presidential race, bringing to the fore a set of divisive social and civil-rights questions that have managed to stay relatively submerged through much of the Reagan era and during the early stages of the 1988 campaign.

For the Democrats, the Bork confirmation battle is an opportunity to define the party's core values. Their most prominent interest groups have noisily joined the fray; the candidates aren't far behind. "This is the sort of fight that reduces everything to the bare essentials," said William Carrick, campaign manager for Rep. Richard A. Gephardt (D-Mo.). "This is what being a Democrat is all about. We can't go into the tank on this one."

The seven candidates, at impromptu news conferences here Wednesday and today, expressed either outright opposition to or deep skepticism about Bork's nomination. While several focused on Bork's role in the Saturday Night Massacre of 1973 in which he fired Watergate special prosecutor Archibald Cox, privately all of them indicated they recognize that the fight is more likely to be waged on the broader, trickier battlefield of ideology.

This presents the Democrats with a dilemma. In the aftermath of their landslide presidential defeats in 1980 and 1984, they have labored to shed their image as a party that is nothing more than the sum of its interest groups. Most have found a new vocabulary to talk about the economy and the role of government. But on questions such as abortion, affirmative action, civil liberties, there's less maneuvering room.

Perhaps because of this, some party leaders, most notably Democratic National Chairman Paul G. Kirk Jr., are not ready to declare the Bork nomination an official "litmus test" of what it means to be a Democrat.

"I don't think that as we move ahead {into the 1988 campaign} we want to necessarily undertake litmus test standards," Kirk said in a post-debate news conference today.

He may fear that if the party is seen in this fight as being driven by aggrieved constituencies -- by gays, feminists and blacks -- it will have trouble attracting the moderate voters it needs throughout the nation, especially in the South, to put together a winning 270 electoral votes.

But for the next 16 months, the image of the party will shaped more by its presidential candidates than by its congressional leadership or its chairman. And Democratic candidates know that the surest way to win primaries and caucuses is to appeal to activist blocs of voters who are major participants in the process.

Some think this does not carry the the risk it may have in the past. "The special-interest albatross has hung most heavily on Democrats when these groups are out there advocating more changes," said former Arizona governor Bruce Babbitt. "What we're talking about with Bork is rolling back the clock. That's what allows the Democrats to step into this one with a lot of vigor. It's not as if we're stapling a wish list together and saying, "What next?"

The stakes are highest for Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.), whose presidential aspirations could hinge on how he handles the Bork fight. But Biden, who said he is deeply skeptical about whether Bork should be confirmed, said today that, his own fortunes aside, he thinks that the struggle could help the Democrats' image.

"I think the vast majority of the American public does not share what I'll refer to as the Rehnquist view of the social history of their nation," Biden said, referring to the conservative chief justice of the United States. "They don't want to go back to the pre-Warren court days.

"If that's the basis on which the fight evolves, I don't think it does hurt the Democratic Party," he added.

Jesse L. Jackson said Supreme Court justices "must have the capacity to make sure that the poorest will be heard." He added that Democrats should not shrink from asserting that view, saying that after 6 1/2 years of the Reagan presidency, "people are more sensitive" to those issues. Jackson said he would oppose Bork on the basis of what he knows now but is prepared to change his mind.

Sen. Paul Simon (D-Ill.), like Biden a presidential candidate and a member of the Judiciary Committee, said he isn't worrying about how the confirmation fight will affect the Democrats. "If the party stands up for what we believe in, we serve ourselves and the nation well," said Simon, who said he has strong reservations about Bork but has not decided how to vote.

Babbitt, Gephardt and Massachusetts Gov. Michael S. Dukakis (D) focused their criticism of Bork on his role as the solicitor general who fired Cox during the Saturday Night Massacre. That focus allows each of them to skirt the issue of ideology in favor of an issue they think will help them in 1988: abuses of power when the Republicans are in charge. Babbitt, calling Bork the "executioner at the Saturday Night Massacre," said the episode is enough to disqualify President Reagan's nominee.

Sen. Albert Gore Jr. (D-Tenn.), expressing doubts about Bork but saying his mind is open, also used the nomination to attack the Reagan administration on the issue of executive branch excesses.