Three units of Harvard's security guards will vote today on whether to form a separate association about two weeks after one of the units defected from Local 254.

If the association is voted down, workers may opt to return to Local 254 or join the Harvard Union of Clerical and Technical Workers (HUCTW).

At stake is the establishment of a group that would be certified by the National Labor Relations Board (NLRB), which under current labor law cannot certify a union which has both guards and non-guards.

Under the old agreement with Local 254, Harvard security guards were not certified because the union included both guards and custodians. But Harvard chose to recognize Local 254 as a viable union.

Many security guards oppose returning to Local 254, which has come under fire from custodial workers for a recent contract that freezes wages for 20 months, reduces vacation time and decreases pay for sick time.

Since security guards paid dues to Local 254 up through last week, many of them think that Local 254 has the first claim on them if the vote for an association does not pass.

"We're hoping this goes through," said a guard who spoke on condition of anonymity. "If it doesn't, we're screwed."

Last month, the NLRB ruled that the three units--Harvard's security guards, parking monitors and museum attendants--could all be classified within the category of guards and therefore could be certified as a union.

According to sources close to the vote, it will be hotly contested. More than 50 percent of the vote is needed for the establishment of the association.

Most of Harvard's approximately 75 security guards will vote in favor of the association, as will a majority of the 15 parking monitors, according to several guards interviewed yesterday.

But sources said a large number of the 40 to 45 museum attendants may vote instead to join HUCTW, for the purpose of gaining member- ship in a much larger group, according to other guards and HUCTW officials. With about 3,500 members, HUCTW is the University's largest union.

HUCTW Director Bill Jaeger said he would welcome the presence of the guards.

"This is a group of people our members consider co-workers," said Jaeger. "I speak for all members of our union when I say we are interested in any type of affiliation."

If the new association is approved today, it would be headed by security guard Stephen G. McCombe, who led a movement for union workers in 1993.

If the association does not pass, guards would not be able to establish a separate association under an NLRB-monitored vote until a year from now, although they would be able to join another union immediately.

Harvard security guards interviewed, none of whom wished to be identified, said almost uniformly that they would vote in favor of the association, primarily because of its guarantees of job security.

"A lot of us have been here long enough," said one guard. "These are the things you bargain for. We don't want to give that back."

Local 254 officials have refused to return repeated phone calls over the past several weeks