"Within a few weeks," promised the campaign letter in October, "just after his return from a state-sponsored economic development trip to the Far East . . . Larry Hogan will formally announce his candidacy" for the U.S. Senate. Hogan's plans called for a helicopter trip around the state, "the fastest and most dramatic way for Larry to share his announcement with the voters of the state," the letter read.

Fully three months after that exuberant message, Prince George's County Executive Lawrence Hogan finally is ready to announce his bid for the U.S. Senate today during the whirlwind tour to Calverton, Baltimore, Salisbury, and Hagerstown that he had canceled at least once before.

"The timing wasn't right" for the trip before, said Hogan's son and spokesman, Lawrence Hogan Jr., who added that today his father also will begin a two-week-long saturation of the Maryland airwaves with between $50,000 and $100,000 worth of television and radio commercials.

If the timing is now right for the announcement, months after Hogan first made known his desire to replace Democrat Paul Sarbanes on Capitol Hill, the times have clearly changed. Hogan, starting with fewer dollars than expected, faces a more vigorous Sarbanes, and the prospect of a fresh-face Republican challenger, former hostage L. Bruce Laingen.

The environment is so different that Republicans wonder aloud whether the aggressive and sometimes strident county executive can be the person to beat Sarbanes.

When he first sounded his challenge to Sarbanes, Hogan said he considered the senator among the most vulnerable of the Democrats seeking reelection. He predicted that the Republican national leadership would make a $250,000 contribution towards turning that Democratic vulnerability into a Republican seat. During the fall, however, the tide began to turn for Sarbanes, whose well-publicized spot at the top of the National Conservative Political Action Committee's "hit list" gave him visibility and a measure of sympathy and support.

NCPAC decided to renew its effort against Sarbanes last Thursday, and is spending $60,000 to $70,000 on another two- week anti-Sarbanes media campaign. A spokesman for the group would not speculate on whether the ads will help or hurt Hogan's chances. "I think it's going to hurt Paul Sarbanes," said NCPAC spokesman Steve DiAngelo, although, DiAngelo said, NCPAC no longer considers Sarbanes its easiest target. "I think there are others that are probably more vulnerable than Sarbanes," he said.

Hogan has publicly distanced himself from that group. ("We wish NCPAC weren't in the state," said his son.) But state Republican leaders acknowledge the very real problems of whether a conservative like Hogan can attract either the party-wide support to carry him through the primary, or general-election crossover votes in overwhelmingly Democratic Maryland.

"He's going to have to offset the anti-labor-union label that some labor leaders who are pro-Sarbanes are going to stick him with," said state Republican chairman Allan Levey. "And he's a fierce competitor. He's going to have to live with that." One Republican state official predicted that "with Hogan, the primary is going to be even tougher than the general," a reference to his unsuccessful governor's race in 1974 when he lost the primary to Louise Gore.

For his part, Hogan, a former FBI man and three-term congressman from Prince George's, seems ready, almost eager, to give up the county executive's chair after months of quiet preparation.

Since last fall, Hogan has been attending political functions around the state three and sometimes four nights each week as well as many afternoons, from Cecil County Republican Club meetings to the Prince George's Black Republicans' Christmas party to the Montgomery Taypayers' League.

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He has surrounded himself with well-known campaign strategists such as pollster Lance Tarrance of Houston and campaign consultant William Lee, who is also acting as his campaign manager. Hogan's 30-second commercials, arranged by media consultant Jay Bryant, are "strictly positive," according to Bryant, and do not even mention Sarbanes. Instead, Bryant said, the commercials emphasize anti-crime legislation that Hogan sponsored while in Congress, and his record for cutting the growth in county spending and taxes since his election as county executive in 1978.

Hogan also has seemed to remove himself from the more acerbic local disputes. Last fall, during one of the most controversial council sessions in years, Hogan was away from the county often, refusing to comment on the actions of an all-Democratic council whose relations with him have ranged over the years from tepid to hostile.

"I think he has deliberately adopted a strategy of low-key non-controversy," said council member Parris Glendening, "One example is redistricting. He just sort of washed his hands of it. Even the cable television, there was one strong blast and that's it." In fact, when the council barely overrode Hogan's veto of a much-criticized cable television franchise award, Hogan was visiting with the Wicomico Republican Central Committee and Republican Club.

"My own sense as chairman was that if you wanted him for anything, you just had to wait," said Glendening, who served as chairman of the council until Dec.1.

Though Hogan has said he is confident about the national level funding after the primary, local money may be a problem. Campaign mailings have flowed steadily from the Hogan headquarters in Clinton, Md., since fall, but Hogan will not disclose how much money he has raised, sparking rumors among Republicans statewide that, whatever the amount, there isn't enough. Hogan's son denied this, saying, "Well, since he's announcing Monday, you can assume he's got the money."

A longtime Hogan friend and contributor, developer Raymond LaPlaca, confirmed that Hogan has not been able to raise money as quickly as he had hoped, "because this is the year of a state election and in Maryland every elective official is running for office and drawing upon finite resources."

Hogan's October campaign letter to contributors described a preliminary collection of $116,511, though Hogan would not confirm the figure. "You'll just have to wait until the filing" with the Federal Election Commission in July, he said through a spokesman.

Sarbanes, whose committee filed a figure of close to $100,000 three months before Hogan's first fundraiser, reportedly had raised $250,000 by late October.

Hogan's fund-raising is well ahead of the only other announced Republican candidate, Silver Spring consultant V. Dallas Merrell, who said that he has raised between $25,000 and $50,000 so far.

Hogan also conducted a poll among voters to evaluate his chances, but consistent with his past practice will not release the results. His son, however, said that while Hogan has extremely high name recognition in Prince George's, he has a high negative rating there as well. He confirmed that Hogan's own poll reflects a statewide indifference to Hogan, particularly when compared to the high favorable rating for the previous frontrunner in the race, U.S. Rep. Marjorie Holt of Anne Arundel County. Holt announced in October that she will forgo the Senate race to seek reeletion to her House seat.

As to concerns voiced by some Republicans that Hogan is not popular enough within his own party statewide, Hogan's son blames the media. "If you repeat a lie enough times, it becomes like the truth, but it's a ridiculous statement," he said, "The facts are that the Republican Party has two times elected him their national committeeman, the state's highest party office. It's kind of hard to say he doesn't have the support of the party.

"Obviously he has some enemies . . . former senator Glenn Beall doesn't like him. Some people say that Allan Levey doesn't like him. But they aren't the party."

National leaders appear to remain enthusiastic. "We're very excited about Larry Hogan as a candidate," said a staff member of the Republican Senate Campaign Committee, "He has a super record of atttacting Democratic votes in Prince George's . . . . He's proven electable."

Yet Glendening, an all-but-declared candidate for county executive, added that he would continue to view Hogan as his opponent for the county executive race next fall, a position echoed by council member Sue Mills, another potential candidate.

"I think he's making a strong effort" in his Senate campaign, said Glendening. "But I just have to believe that when push comes to shove he'll look at those numbers and realize he can't win in Baltimore City, and come back and run for executive."