For the fourth time in less than two years, it appears that key politicians are not going to be able to make good on a promise to the securities industry.

Faced with a threatened filibuster, the Senate leadership yesterday pulled legislation off the floor that would have lowered the capital gains holding period from one year to six months, a proposal that has become one of the most heavily used bargaining chips on Capitol Hill.

"We've been up the mountain on a number of occasions," Stephan K. Small, vice president and director of congressional relations for the Securities Industry Association (SIA), said. "If I was detached from the issue, I might see some humor in it."

According to estimates by the securities industry, the bill would result in the purchase of at least $50 billion more worth of stock and other securities -- a development that would also result in significantly increased commissions to stockbrokers.

Liberals, however, say the change would reduce capital gains taxes by at least $200-million-a-year, a bonanza primarily for the wealthiest taxpayers and just the kind of tax change that the voters signaled their opposition to in the last election.

The history of this legislation is one of the most bizarre in recent memory:

In 1981, the SIA cut a deal with the Reagan administration. In return for getting the capital gains provision added to the $749 billion tax cut, the SIA would mobilize stockbrokers across the country to lobby for the administration-backed tax bill, and in opposition to the Democratic tax proposal before the House.

The SIA followed through on its half of the bargain, generating an estimated 20,000 telephone calls to members of the House. But when the tax bill went to a conference committee, Rep. Daniel Rostenkowski (D-Ill.), chairman of the Ways and Means Committee, cut the provision from the legislation.

Then, last summer, Sen. Robert Dole (R-Kan.), chairman of the Finance Committee, negotiated a second deal: if the securities industry would back the $98.3 billion tax increase, including the painful section requiring 10 percent withholding on dividend income, then Dole would add the capital gains provision.

This time, the SIA again kept its part of the bargain, Dole did add the provision, only to see Rostenkowski submarine the arrangement for a second time.

Rostenkowski refused to play ball in large part because one of the key proponents of the capital gains change was Rep. Kent Hance (D-Tex.), who was the only Democratic member of the Ways and Means Committee to support the 1981 Reagan tax bill, co-sponsoring the measure and giving it at least a patina of bipartisan support.

Rostenkowski told Dole "we would stay in conference forever if the Senate insisted on keeping that provision, not because of the merits of the provision but because of the author Hance of that provision," Dole told his Senate colleagues.

Committed to keep his promise to the SIA, Dole in August pressed forward and won Senate approval to add the capital gains provision to the debt ceiling bill by a vote of 77 to 17, only to see the move collapse when congressional leaders decided that the only way to get the debt bill passed was as a "clean" bill without amendments.

His most recent move has been to add the capital gains section to a bill relieving California utilies of a potential tax bite of $2.2 billion, a measure with strong House support and strong backing by members of the California delegation.

Yesterday, however, when he sought to bring the bill to the floor, Sen. Dale Bumpers (D-Ark.) immediately began a filibuster and, after three hours, Sen. Howard H. Baker Jr. (R-Tenn.), the majority leader, pulled the bill from the floor.

"It's too early for the dirges to begin," Small of the SIA said. Others, however, suggested that the bill is in serious trouble, and even if it gets through the Senate opposition, it faces an uphill battle in the House.