As if the gender gap were not enough to fuel conversation this autumn in the political hot-stove league, the Democratic Party fans now have "The Glenn Gap" to puzzle over.

The Glenn Gap is the distance between presidential candidate Sen. John Glenn's strength in public opinion polls and his scant support visible when Democratic Party workers gather. The gap was acute and much discussed at the New Hampshire Democratic Convention here Saturday.

The latest published poll of New Hampshire Democrats, taken in early October, showed the Ohio senator running second to former vice president Walter F. Mondale, with the other Democratic hopefuls trailing far behind. Mondale had 44 percent and Glenn 20 percent in the poll taken for Manchester television station WMUR.

But an applause meter in the gymnasium of New Hampshire College, where more than 1,500 delegates, alternates, and guests heard the seven announced Democratic candidates in a 90-minute forum, would have placed Glenn far behind not only Mondale, but Sens. Gary Hart (D-Colo.), Alan Cranston (D-Calif.), and former senator George McGovern (D-S.D.).

Mondale, Hart and Cranston all had vocal, organized supporters to cheer them into the hall. McGovern, whose late entry into the race has precluded real organizing, nonetheless got an affectionate and prolonged welcome from the delegates--many of whom came into politics during his 1972 campaign here for the presidential nomination and against the Vietnam war.

Glenn's presence caused no more of a ripple than those of long shots Sen. Ernest F. Hollings (D-S.C.) and former Florida governor Reubin Askew.

In his speech and answers to questions, Glenn struck neutral observers as being as polished as any of the others except Hart--who had a very good day in the state where he has perhaps his best support.

Yet the response to Glenn was negligible. Indeed, when some in the audience were booing his defense of his vote for the 1981 Reagan tax bill, there was not enough of a Glenn claque to drown it out.

The pattern here was not much different from state conventions this fall in such other early delegate-selection states as Maine, Iowa and Florida. But in some ways, it was even more troubling to Glenn backers.

While the New Hampshire convention-goers were more liberal than the state's Democratic electorate, they still represented a cross-section of party activists here--the people who provide the core of workers in most campaigns.

Particularly notable was the absence of any sizable Glenn contingent from Manchester, a city whose Democratic voters and politicians range from moderate to very conservative. Although the convention on the outskirts of this city was ideally situated from Glenn's political point of view, no one had organized a turnout of those presumable backers.

Gloom was evident at the table of Glenn supporters at a fund-raising dinner Saturday night attended by all the candidates except Glenn, who had left to keep a commitment in West Virginia.

"This has been a real downer for us," one of Glenn's top supporters in the state said. "I'm not a summer soldier and I'm not going to quit. But some of the Manchester politicians who signed on with Glenn because they thought he was a winner are really wondering if they are going to be left out on the limb."

Adding to concerns was the resignation, two days before the state convention, of J. Joseph Grandmaison as national field director of the Glenn campaign. Grandmaison, of nearby Nashua, is well-known to New Hampshire Democrats for his organizing skill and quick temper--and for being the Glenn camp's main advocate of the importance of local organizations.

New Hampshire Democrats were asking reporters if Grandmaison's departure meant that Glenn would rely on television advertising to try to win the primary--a policy they think unwise.

Glenn has campaigned much less intensively in New Hampshire than have other candidates. According to Chris Black of The Boston Globe, Glenn has spent eight days in New Hampshire, compared with 20 for Mondale and 28 for Hart, and even more for some others.

Before he left the campaign, Grandmaison said the senator had been forced to give priority to fund-raising and to initial contact work across the country in order to recruit top-level steering committees in more than 30 states. He said intensive organizing in the early primary states would begin soon.

That promise has been repeated by Grandmaison's successor, Robert J. Keefe. Top Glenn supporters in New Hampshire said they know Keefe only by reputation, and some of them mentioned that in the last presidential campaign that he ran, the late senator Henry M. Jackson's in 1976, Keefe bypassed New Hampshire and concentrated on winning Massachusetts.

Still, Rich Jenkinson, Glenn's state coordinator, said he expected to have a full-scale Glenn organization in place by Dec. 15.

If that is done, most New Hampshire observers still think Glenn can become a major factor in the primary, which will be Feb. 28 or March 6. The state's Democrats have a history of favoring the more moderate-conservative candidate. Mondale faces a potential problem in the splintering of the liberal vote among Hart, Cranston, McGovern and himself--the same pattern that let Jimmy Carter win a plurality over four more liberal rivals in 1976.

A Cranston supporter said Saturday night that many of the Manchester Democrats backing Rep. Norman E. D'Amours' (D-N.H.) bid for the Senate believe that Glenn on top of the ticket would help their man much more than Mondale would.

"John Glenn probably gets 20 percent of the vote just by putting his name on the ballot," this man said.

He quickly added that going beyond that base would require Glenn to devote time and organization effort to New Hampshire that he has not committed so far.

The lack of that effort was the most conspicuous fact Saturday at the convention and is the probable explanation for the "Glenn Gap."