Robert M. Tobias is betting his future on Social Security.

As president of the National Treasury Employees Union (NTEU), Tobias, 44, has begun the long campaign to wrestle union representation of the Social Security Administration (SSA) away from the rival American Federation of Government Employees. He said he is convinced that he can do it.

Organizationally, Tobias said, the SSA is the government agency most like the Internal Revenue Service, which comprises the bulk of NTEU membership. "Social Security is the best fit," Tobias said. "There's no other fit like it."

By organizing the SSA, Tobias could nearly double the number of people his union represents and probably double the number of dues-paying members.

To bolster their image, federal employee unions talk in terms of workers they represent rather than members who pay dues.

The NTEU, for example, bargains for 130,000 persons, but only 65,000 of them belong to the union. Similarly, the AFGE talks of representing about 700,000 workers, but only 207,000 pay union dues.

"I consider this to be a long-term campaign," Tobias said of the effort to organize the SSA. "We've hired a group of organizers, a really crack group of organizers, and we've been communicating regularly with SSA employees and leaders."

Although some organizers are in the field, Tobias said it would be several years before the NTEU seeks union recognition at the SSA.

Under federal labor-relations law, a union can seek to win representation from another union only during a specified "open period" at the end of a labor contract. The current AFGE contract with the Social Security Administration expires in June with the open period beginning this spring.

Tobias said he does not think that he will be ready by then: "We're looking to 1990 or 1991."

That timetable could quickly change, however, if the AFGE falters in its negotiations with the SSA. Open season for representation elections continues until a new contract agreement is reached.

If the AFGE fails to win a new agreement by the June deadline and negotiations drag into the summer, there are indications that the NTEU might change its timetable.

The AFGE has sent its initial bargaining proposal to the SSA, but a union official said the agency replied that it was too early. The AFGE apparently is not unaware of the stakes in the forthcoming negotiations. "We know we have to do a good job," the official said.

The AFGE also faces financial problems as it prepares to battle both the SSA and the NTEU. Late last year, the union was so strapped for cash that it sought a rescue from the AFL-CIO. The AFL-CIO and four member unions gathered a $1.5 million loan package to help the AFGE organize new members.

The AFGE plans to seek a dues increase at its summer convention. If that fails, the AFL-CIO unions are not expected to lend more money.

Tobias said he thinks unions that participated in the loan program did so as insurance in case the AFGE is forced to seek a merger partner.

If the AFGE fails to gain a dues increase and is still negotiating with the SSA, the NTEU may decide to step up its organizing drive, according to union officials.

Whenever the NTEU decides to make its run at the SSA, the first target will be agency headquarters, which has about 15,000 employees in Baltimore. If it succeeds there, the NTEU then will pursue all other SSA units.

"SSA is one unit nationwide," Tobias said. "It consists of the headquarters, their district employees and the payment-center employees." The NTEU already represents regional SSA employees formerly represented by the AFGE.

The NTEU basically sells itself as the white-collar union of federal employees, and Tobias said he thinks that will help its efforts to organize the SSA.

He would not discuss other future organizing targets and said his union is not interested in organizing blue-collar wage earners. "Our goal is to continue to expand among general-schedule employees," he said.