Five-term conservative Rep. Marjorie S. Holt (R-Md.) said yesterday she is building a statewide precinct organization and raising money with the idea of challenging Sen. Paul S. Sarbanes (D-Md.) next year.

Holt, encouraged by results of two polls and bolstered by appearances at dozens of meetings around Maryland, said she hasn't decided yet, but added, "in politics, timing is everything, so you like to get in early."

In recent weeks, the Anne Arundel County representative has conferred with state and national party leaders and appeared at more than a dozen Lincoln Day dinners across the state, apparently clearing the way for an unopposed bid for the nomination.

"If Maryland continues to approve of the Reagan administration, I'm in a good position," Holt said during an interview in her congresional office. "But Maryland has to be exactly right. If the people suddenly are unhappy" with the president, the chances of any Republican beating Sarbanes are slim, she said.

Alan C. Levey, the Republican state chairman, said he will meet with Holt next week to urge her to make her final decision sometime this summer.

"She looks like the person most able to beat Paul Sarbanes," Levey said, "but to do that, irregardless of what Sarbanes believes, she must start soon. It will be a long, expensive battle."

Levey was referring to complaints by Sarbanes last month that an advertising campaign directed against him has forced him to think about his reelection campaign much sooner than he would like.

Sarbanes' press secretary, Bruce Frame, said yesterday that because of the anti-Sarbanes television and raido campaign by National Conservative Political Action Committee (NCPAC), the liberal Democrat has "began planning earlier than expected, but other than that, he has done nothing dramatic."

Levey said that as state chairman "I must remain neutral" about who gets the nomination, but he added, "she'd be the odds-on favorite in a primary."

Levey wants Holt to decide before the end of the summer, both so the party can find someone to replace her as a House candidate, and to have time "to make her a household name" throughout the state.

A poll commissioned by Holt, and conducted by Richard B. Wirthlin, who also is President Reagan's pollster, found that as of the end of March, Sarbanes led Holt by 44 percent to 40 percent.

Wirthlin pollsters telephoned 800 Maryland residents March 27 through 29 (just before the attempted assassination of President Reagan and long before the anti-Sarbanes ads). Sarbanes' 44-to-40 edge was among the 75 percent who had heard of Holt.

Holt, 60, said she had been "hoping that the poll would come back so bad" that she would not be enticed into giving up the safety of her House seat to run statewide.

"Maryland is a very liberal state," she said. "If I lived in Texas or Tennessee, I'd already be running like crazy" for the Senate.

While she acknowledges that she is a conservative, Holt said that the poll showed that "I'm perceived as a moderate," which "gives me a better opportunity to approach a wider range of voters."

A more recent poll, conducted by Arthur J. Finkelstein, also showed Holt within four points of Sarbanes. according to Levey. The Holt-Sarbanes portion of the Finkelstein poll was financed by NCPAC and was taken after it sponsored the series of anti-Sarbanes ads in Washington and Baltimore. Levey said an earlier Finkelstien poll showed Sarbanes with a seven-point lead.

While one Sarbanes supporter scoffed at "releasing results of selfserving polls," he said and the freshman senator would "relish" an announcement by Holt that she was going to challenge him. "Who would you rather face, Marjorie Holt or Bruce Laingen?" he asked rhetorically.

He was referring to reports that Laingen, the highest ranking State Department official held hostage in Iran, is weighing suggestions that he seek political office. Laingen, a resident of Bethesda, has been proposed as a potential opponent of Sarbanes, running as a Republican. But another report was that former Vice President Walter Mondale has urged Laingen to run as a Democrat in his native Minnesota against Sen. David F. Durenberger. Laingen declined to comment yesterday on either report.

Holt said the NCPAC ad campaign is "the greatest thing Sarbanes has going for him. It's getting him money and sympathy, and he's started to work. For the first time in more than four years, people are starting to hear from him," she said.

For most of her 10 years in Congress, Holt was overshadowed by her flamboyant, conservative counterpart in the Maryland delegation, Robert E. Bauman. But Bauman's defeat last November, following his admission of homosexual and alcoholic problems, "cleared the way for me," she acknowledged.