ANNAPOLIS, JUNE 29 -- Maryland Republican gubernatorial candidate William S. Shepard has picked his wife, Lois, to run for lieutenant governor with him in the November election, an unprecedented move that prominent Republican Party leaders believe will make Shepard's longshot campaign even more difficult.

Shepard, 55, a former diplomat from Potomac, defended the decision today, saying that his wife of 30 years was always among his top choices, even though he didn't offer her the job until two other Republicans turned him down.

"I have always had Lois in mind because she is a very substantive person," Shepard said of his wife, a former teacher, political activist and former director of the federal Institute of Museum Services.

"The question came down to this: Do I want someone on the ticket merely for the sake of filling out a ticket . . . or do I really want to stick to my substantive guns?

"In a sense she was my first choice, but in a real political choice she was my last . . . because of the possible reaction."

Lois Shepard, 52, said, "I think this is dynamite . . . . I have not had such a compliment since he asked me to marry him." She said the family ticket represents "a breakthrough for women in Maryland and maybe all over the country . . . . For so many years women have been behind their men, it is time in the 1990s that they be beside them."

Other Republicans, however, were glum. Few believed that Shepard would defeat Democratic Gov. William Donald Schaefer, but party leaders hailed Shepard as a credible spokesman for a party that seems always faced with controversy.

"I had no reason to change that assessment until today," said state Sen. John N. Bambacus (R-Garrett). "It is almost ridiculous to have a husband and wife running. This is serious business, and Republicans have enough trouble in Maryland struggling to maintain a credible second party."

Bambacus and others said that aside from being an unconventional choice, Shepard's decision to run with his wife brings none of the traditional geographic or political balance to a ticket typically looked for in a lieutenant governor; another woman, they said, could have filled that need along with reaching out to women voters.

"This ticket is not going to go over well. It just does not set well with people," said Rep. Helen Delich Bentley, the party's top elected official and senior congresswoman. Telephone calls to her office "are not good. "I don't think it will help the party. I'm as concerned about that as anything."

Schaefer, asked about his opponents by a reporter from the Baltimore Sun when he returned from a trip to Europe, reportedly chuckled and said, "That's very nice."

Today, Schaefer campaign workers were harsher.

Said Schaefer campaign manager Jim Smith: "What they hope to present to the voters are two people who have absolutely no experience in Maryland state government."

The Maryland GOP has been struggling in recent years, split in a virtual civil war between moderates and conservatives. The party's 1986 gubernatorial candidate received less than 18 percent of the vote, and its U.S. Senate nominee in 1988 dropped out of the race.

New party Chairwoman Joyce L. Terhes has succeeded in getting the party out of debt, and is searching for ways to translate its gains in voter registration into success at the polls. While the GOP has delivered the state for Republican presidential candidates, Democrats still hold an overwhelming advantage in the State House and on county councils throughout Maryland.

Shepard's campaign is seen among Republicans as a longshot, but it was thought he would at least divert some of Schaefer's substantial campaign treasury and help excite local Republicans.

With the choice of his wife, some Republicans are wondering if that opportunity has been lost.

"Let's be honest, I think it hurts his chances," said Sen. Lewis R. Riley (R-Wicomico). "No disrespect to his wife, but it is a political mistake."

Terhes said she was also uncomfortable with the idea at first, and encouraged Shepard to reconsider and interview some other candidates. But now that the decision is made, she said the party should be thankful it has two qualified candidates for the state's highest office -- even if they are married.

"It would not have been my choice, but if that is what he is comfortable with that is his decision," Terhes said. "It is done and we have got tremendous candidates."

With a 9 p.m. Monday filing deadline closing in, Shepard had to make a decision; the Maryland state constitution requires gubernatorial candidates to name a running mate when they file. That law has forced some candidates into uncomfortable circumstances. Former governor Harry Hughes's alliance with Samuel Bogley, for example, ended with the two not speaking to each other.

The Shepards, who married after a Harvard-Vassar courtship and celebrated their 30th anniversary this week, said they don't think politicking together will strain their relationship.

"I think it is wonderful," said Marie Morse, political director with the National Women's Political Caucus. "Most male governors have had their wives as support and helpmate, this one is making it official."