He is counting on the popularity of Gov. Harry R. Hughes, Sen. Paul S. Sarbanes and Rep. Michael D. Barnes--along with anti-Reagan sentiment--to propel him to victory in the race for Montgomery County executive.

Sounds like a reasonable scenario for Democratic incumbent Charles Gilchrist, but the game plan being described is that of Gilchrist's likely Republican opponent, Del. Luiz Simmons.

Simmons, a 33-year-old, one-term member of the House of Delegates, was to announce his candidacy yesterday, and while he didn't plan to unveil his elephant-in-donkey's-clothing strategy, he said in an interview last week that he is counting on the reluctance of Montgomery Countians to vote a straight ticket to help him defeat Gilchrist.

He sees himself as the inheritor of the Gude-Mathias-Steers--and he should add Jim Gleason--tradition of moderate Republicans who have been elected by conscience-stricken Montgomery Democrats who worry that straight-party voting reflects the mindless obedience of big-city machines that many of them grew up with.

"People want to split their ticket," Simmons said, "and they'll look for the weak link in the Democratic lineup. I think that's Charlie. He is a nice man, but he was an undistinguished legislator and he's been an indecisive executive."

The big trick that Simmons hopes to pull off is to saddle his Democratic opponent with the sins of his Republican president.

"The last two presidents have attacked the federal workers, and Charlie has let them get away with it," Simmons said. "If a president went to California and attacked the aerospace workers, or to Detroit and criticized auto workers, he'd be run out of town, and the local officials would be leading the way. But not Charlie, even though public service is the principal industry of Montgomery County."

Simmons admits that part of the motivation is to "link Reagan to Gilchrist before Gilchrist puts him on me."

Dumping on a conservative Republican president--even if he is the leader of Simmons' party--isn't the dumbest strategy in a county where registered Democrats outnumber Republicans 2 to 1.

Republicans in Montgomery "are survivors," said Simmons, who suggested that Democrats, because of the big bulge in registration, can afford to make mistakes. "But if you are a Republican, the margin of error is small--do one wrong thing and you lose."

Simmons learned that political lesson early, growing up on Long Island (although he was born in a hospital in Winchester, Va., and his parents lived briefly in Hagerstown) as an Eisenhower-Javits-Rockefeller Republican.

He also learned about disappointment. "My life has been a series of small rejections," is how he put it. Beginning with college, where his father, who sold ads for the Yellow Pages, wanted him to follow in his footsteps at Yale, "but I couldn't get in." So he came to American University, where he was elected student body president in 1968 and graduated in 1970.

After short stints on the Hill "working for the only Jewish Republican in the New York delegation" and for the White House Conference on Children and Youth, in 1972 he returned to AU as a law student, got married, moved to Montgomery County and registered to vote, declining to state a party preference.

Two years later, with a law degree in hand, Simmons changed his registration to Republican and filed as a candidate for the General Assembly. He was nominated in the primary but--another "small rejection"--he lost in a Democratic sweep of his Rockville district in November.

Four years later, with the memory of Watergate dimmed, he campaigned again and won, becoming one of only four Republicans in the 25-member Montgomery legislative delegation.

With such a fast start, Simmons worries that Gilchrist and other political detractors "may try to paint me as another Lanny Davis" (a smart young lawyer whose defeat in a run for Congress was blamed on an image of being too eager, too ambitious). "But that won't fly," predicted Simmons. "I've been married 11 years, got two kids, a big mortgage, and a legislative record."

The latter, he said, includes requiring gas stations to post prices and a generic drug law that is a model for the nation.

Simmons said he is "serene" about the campaign, even though he realizes that because he is giving up his legislative seat he'll be out of public life "for a long time" if he loses. But he said he is prepared for that. It would be just another "small rejection" that he would soon get over.