Rep. J.J. Pickle is a polite, garrulous, 67-year-old Texan, who is obsessed by Social Security, about which he knows more than any man on Capitol Hill. He is chairman of the Social Security subcommittee of the House, and to some Democrats his counsel on the troubled system is as sour as his name.

Pickle is admired by his colleagues for his knowledge and devotion. But they sigh that he is "a political innocent" who cannot grasp the importance of exploiting Ronald Reagan's egregious blunder on Social Security.

Pickle, in leadership councils, keeps pressing statesmanship on his fellow Democrats, and reminds them that as inventors of Social Security they have a moral obligation to save it. The Democrats' inclination is to patch up the system this year and leave what Pickle regards as essential reforms for another time.

If the "bipartisan" approach which Reagan is belatedly urging on them were to succeed, the president would share the credit for the rescue of a government program which he has throughout his political career regarded as, in the words of a new labor ad, "a handout, not a contract."

Pickle is often reproved for his willingness to play ball with Republicans, but he stubbornly maintains that Democrats will pay a higher price for embarrassing Reagan than for straightening out the Social Security's tangled financial situation.

The struggle for the soul of Speaker Thomas P. O'Neill (D-Mass.) has been raging for several months. A coalition of outside experts led by former HEW secretary Wilbur Cohen and former Social Security commissioner Bob Ball contends that with borrowing from the Hospital Insurance Fund, the benefits can be paid as before.

Pickle, although reluctant, he says, to be "negative and argumentative towards my leadership," insists that it is "not enough."

O'Neill is indicating that Bob Ball will carry the day, that the Democrats will refuse Ronald Reagan's new invitation to the waltz.

Nothing that Reagan has said or done about Social Security since his disastrous spring offensive indicates that he wants to do anything more than damage control --and to spike charges that he is going to meet his receding figure of a $42.5 billion deficit by short-changing the seniors.

He has, according to spokesman David Gergen, "no plans" for cuts in benefits--beyond what he has already proposed. And Gergen was careful to say that the president has not abandoned his idea of penalizing, beginning in January, those who retire at age 62 and eliminating payments to those 3 million Americans who are raking in $122 a month in minimum Social Security payments although they do not "deserve" to.

His idea of putting a safety net under the "truly needy" among minimum recipients by sending them to the welfare office to apply for benefits has dented his image as a kindly fellow, and an antagonist of welfare.

Adding to the grotesque nature of the notion is a new directive from the Department of Health and Human Services that reduces from $2,000 to $1,000 the amount of non-essential property allowed to potential recipients. Would a 90-year-old lady have to give up her parrot or her parrot-cage, or both, to qualify for assistance?

Naturally, Reagan would like the Democrats to help him scotch this kind of "Saturday Night Live" travesty. Understandably, they would rather not--if they can be sure that seniors will not suspect them of playing politics with their golden years.

Social Security was not discussed at the "harmony" caucus where Democrats decided they would not punish their Reagan defectors without due notice. It probably would have been as divisive a question as could have been raised.

Some Democrats charge that administration "ghost stories" about the imminent bankruptcy of Social Security have created a panic among all ages-- present and prospective recipients and many people of middle years who have called up Pickle to lament that Mom and Dad will have to move back home if the checks shrink or disappear.

"They have destroyed the climate for reform," says one of O'Neill's staff. "People are so frightened that they think when you say 'reform,' you really are talking about reduced benefits."

Democrats also complain that when Reagan successfully peddled tax cuts, he gave a rosy view of the economy. But when he talks about Social Security's future, he paints it black.

But Pickle, who concedes that "inter-fund borrowing" might keep the system going until 1986--at least in the absence of severe economic reverses--says it is so "risky" that it will further lower public confidence in Social Security.

Everyone agrees that if reforms fail this fall, they will be put off indefinitely. Controversial measures are always passed over in a campaign year, and in the event the Republicans take control of the House, Social Security will not be a high-priority item, and Reagan could boldly suggest to nervous citizens that private annuities are much more reliable.

The temptation to do otherwise is enormous, but Pickle says the Democrats must do the decent thing. If he weren't around, they might not even consider it.