Even though Maryland House Speaker Benjamin L. Cardin was running dead last in a three-way race when he ended his campaign for governor last week, his decision to campaign instead for Congress has altered the face of the State House race for the two candidates who remain.

For the first time since maneuvering began earlier this year for the 1986 elections, the top two contenders for the Democratic nomination -- Attorney General Stephen H. Sachs and Baltimore Mayor William Donald Schaefer -- are free to spar directly with each other.

"Today, [Cardin's withdrawal] doesn't make very much difference, but in terms of potential, it brings the race into sharper focus," Sachs said after Cardin's announcement last week. "To challenge a celebrity like the mayor requires a sharp focus."

Schaefer said in an interview before Cardin's announcement, which was expected at the time, that it would have been difficult for voters to differentiate between himself and Cardin, who is also from Baltimore, because both have drawn support from the same organizations in the past. He would not speculate on whether Cardin's withdrawal would aid his own candidacy.

But James W. Smith, a Baltimore businessman and a key Schaefer aide, said last week that after Cardin's announcement he received calls from people interested in joining the Schaefer campaign.

"While the polls, to the extent that they're accurate, don't indicate he had wide support, he certainly had attracted very good people to his campaign," said Smith. "We clearly hope now to win the support of as many of those people as possible. The indications are very good that we'll be able to do that."

Not everyone agrees with Smith's optimism. Sachs said that he had decided months ago to base his campaign on the assumption that Schaefer would be his only significant opposition.

"Ben's constituency was not so wide that you could talk about a constituency who would move," Sachs said. In any case, he said, "the phone has not been jumping off the hook" with Cardin supporters calling to campaign for him.

For some Cardin backers, such as Baltimore Del. Paul Weisengoff, the choice was clear: "I'd support the mayor in a minute," he said before Cardin switched races.

"There are lots of people that would like to support the mayor who are supporting Ben," he added. "Ben's getting out gives the mayor more support."

For others, especially elected officials in the Washington suburbs, the options are murkier. House Majority Leader Donald B. Robertson (D-Montgomery), an ardent Cardin supporter, said he is still getting used to the idea that his candidate is no longer in the race. Weisengoff's theory, he said, is incorrect.

"It may be true of the people that Paul knows, but of the people I know, some will go with the mayor and some will go with the attorney general," he said.

State Sen. Decatur Trotter (D-Prince George's) said that he had adopted a wait-and-see posture. "A lot of things will be happening during the [General Assembly] session that depends on who you're supporting for governor," he said. "You have to be careful about jumping out there supporting somebody."

Similarly cautious is Ida Ruben, who heads the Montgomery County House delegation and is running for the state Senate seat being vacated by 8th District congressional candidate Stewart Bainum Jr.

"I'm on neither side at this point," said Ruben, who was in attendance at Cardin's official announcement last week in Baltimore. To support either Sachs or Schaefer, she said, would "alienate some of my supporters."

But both sides agree that it is still too early in the process for either side to know what will happen between now and the June filing deadline.

"Most Marylanders are not politicians, political junkies, journalists or . . . even on the edge of becoming interested in politics" yet, said Sachs.

Added Smith of the Schaefer camp, "We have a little over 6 1/2 months to go before the filing deadline. My experience in politics tells me that it is very presumptuous to say no one else is going to file."