The tempo of the Democratic race for Montgomery County executive picked up yesterday as three candidates, sharing the view that they are in a dead heat, campaigned furiously among the enormous crop of undecided voters who will determine the outcome of Tuesday's primary election.

The pace was accelerated by the Montgomery County Sentinel newspaper's published poll showing that more than half the voters have still not made up their minds. The poll, conducted within the past week, gave State Senator Charles Gilchrist and county Planning Board Chairman Royce Hanson each 15 percent of the vote and County Council member John Menke 14 percent, with 55 percent undecided.

"Everyone is looking for a rabbit to pull out of a hat to put them ahead," said one of Menke's supporters.

In the late afternoon, the Menke camp let it be known that outgoing Republican County Executive James P. Gleason was about to publicly throw his support behind Menke.

An angry Gleason confronted reporters with a denial that he had never said such a thing. "I'm not endorsing in the primary. I never told anyone I was endorsing in the primary. I may not even endorse in the general election. I'm not expressing my feeling publicly," said Gleason, the county's first and only executive. He has decided to retire from the office after eight years.

Gleason said he had met with Menke yesterday and that Menke's supporters had "talked to me a couple of times" about a possible endorsement. "But they never asked for my endorsement," said Gleason.

Although Gleason said he did not intend to get involved in the race, he attempted earlier this year to find a strong candidate to run against Richmond M. Keeney, a former county councilman and a current planning board member who is considered the front-runner among the three Republicians vying for the county executive nomination.

Meanwhile, the three tired Democratic contenders in the executive's race went to coffees, senior citizens luncheons and shopping centers to seek out votes. Republicans Keeney, Albert Ceccone and Gerald Warren had light campaign schedules during the day but planned appearances, at the Potomac Republican Women's Club last night.

Hanson, buoyed by the endorsement of the Montgomery Sentinal, admitted cheerfully at a morning coffee in Potomac that he already was a "zombie . . . being held up by orange juice and support hose."

Although the tone of the campaign has remained gentlemanly and no candidate has lambasted his opponents, Hanson has stressed his management experience, which he considers to be his chief asset.

The Sentinel called both Menke and Hanson "qualified to be county executive, "but chose Hanson because of his "longer experience in the county government and the political arena and because we believe he would be a stronger, firmer leader."

"I normally have more executive experience before lunch than my two opponents have had in their entire careers," Hanson said. He has chaired the Maryland-National Park and Planning Commission for five years.

Gilchrist began his four-evening appearances at River Road Unitarian Church with a pep rally of 300 supporters who cheered him on with their beer and balloons. "I will be the next county executive," Gilchrist confidently told the jubilant crowd.