Maryland Republicans, who have been scouring the state for almost a year for someone to be their standard-bearer in the 1986 election, acquired a gubernatorial candidate today. But GOP officeholders and party leaders responded to the welcome news by being elsewhere when Del. Thomas J. Mooney announced his candidacy here.

Mooney, 41, a two-term Takoma Park legislator who defected from the Democratic Party last fall, threw his newly acquired GOP hat into the gubernatorial ring by proclaiming that the race for the State House "will be uphill but not impossible."

Mooney, who has a reputation as a somewhat unconventional lawmaker who frequently proposes legislation that draws attention but rarely passes, promised to run a "people-to-people" campaign whose centerpiece would be a walk across the state "from Oakland to Ocean City."

With his wife Elaine by his side, Mooney suggested that the true importance of his long-shot candidacy may be in helping rebuild the Maryland Republican Party. The party, which carried the state for Reagan in 1984, still suffers a 3-to-1 Democratic edge in voter registration.

The GOP has not held the State House since Spiro Agnew left office in 1969, and it is vastly outnumbered in the General Assembly.

If Mooney is the best hope for a GOP resurgence, it was not evident at his announcement today at state party headquarters. Not a single Republican officeholder was there for the kickoff, and the only party official in attendance was the GOP executive director.

To run in a year when the Democratic gubernatorial primary includes two proven vote getters -- Baltimore Mayor William Donald Schaefer and Attorney General Stephen H. Sachs -- GOP leaders had pinned their hopes on Howard County Executive J. Hugh Nichols.

But Nichols, also a Democrat-turned-Republican, abandoned that quest early this year when he became convinced that Schaefer was drying up most of the available money from the business community.

The GOP has two credible U.S. Senate candidates -- Linda Chavez and Richard Sullivan -- but the party's gubernatorial contender, who will be at the head of the ticket, has little name recognition and dim prospects of raising money. Mooney's difficulties within his own party were reflected in a response by state Sen. Howard A. Denis (R-Montgomery) when he was asked today why he didn't attend the announcement: "I have my own race to worry about."

A conservative legislator who has been an ardent foe of abortion during his time in Annapolis, Mooney won election to the House of Delegates in 1978 by bucking the Prince George's County Democratic organization. He was narrowly reelected four years later, coming within 10 votes of losing the primary.

Mooney said today he was proudest of his legislative work on behalf of utility rate reform. But he is better known for sponsoring measures to legalize gambling and for bills that would require thumbless boxing gloves and allow movie patrons to bring their own snacks to theaters.

Allan C. Levey, chairman of the Maryland Republican Party, said today that "the kind of campaign Tom Mooney will run will help Republican candidates all over Maryland. He's not going to have much money to work with, so he's going to have to do it on an individual basis, but nobody will work harder than he will."

When asked why he didn't attend Mooney's announcement today, Levey, who is a dentist, said he was busy "pulling teeth."