Houston attorney Leon Jaworski announced here yesterday that he will chair a national "Democrats for Reagan" committee. In standard news conference fashion, he read a statement and then took questions from reporters. cThat's when the trouble began.

For the next half-hour, the former special prosecutor withstood a hurricane of hostile questions from a press corps that was clearly dubious about some basic points, including whether Jaworski is really a Democrat, whether he is really for Ronald Reagan, and whether there really is a committee.

Jaworski, who gained national fame as chief investigator of the Watergate and Koreagate scandals, announced the formation of "Democrats for Reagan" in a brief statement that said nothing positive about Reagan, focusing instead on harsh criticism of President Carter's handling of his brother's ties to Libya.

When Jaworski finished, the reporters began asking him to reconcile his support for Reagan with a speech he gave April 28.

Jaworski was supporting George Bush for president then, and he called Reagan an "extremist" who offered "simplistic remedies and shop-worn platitudes." He also noted that Reagan "has had no experience -- absolutely none -- on the national level, and no experience -- absolutely none -- in foreign affairs."

Today, Jaworski first said there was a "short answer" to explain his change of view: "I would rather have a competent extremist than an incompetent moderate."

As soon as he uttered this, however, he expanded on the answer, saying that he now considers Reagan a "moderate." Reagan has proven this, Jaworski said, by his choice of Bush for vice president and by his commitment to "surround himself with the best minds in every field."

Next the reporters moved on to queries about Jaworski's political status. How could he be a "Democrat," they asked, when he campaigned for Republican Bush last spring? The white-haired lawyer responded that he was a "registered Democrat" who over the years had supported candidates from both parties.

The reporters persisted. Which party's primary had he voted in this year? Jaworski shuffled uncomfortably, cleared his throat, stammered, "I did not vote at all," he said.

The next line of questioning dealt with the committee Jaworski will chair. Where will it operate? How much will it spend, and for what? Jaworski admitted that he had no answers.

"Are there any other members of the committee?" he was asked, and again he was unable to say. Looking plaintively at the Reagan campaign staffers in the back of the room, the former special prosecutor answered, "They have some, but I don't know who they are."

Reagan's national political coordinator, Donald Lukens, said later that the committee would include prominent Democrats from 30 states and would operate in major states that are expected to be closely contested.

In his comments on the Billy Carter affair, Jaworski said it suggested that the White House has a "system of keeping things from the public." He said this has "contributed to the casting of a cloud of suspicion over the presidency."