A small group of gamblers, most of them members of one family, rigged the Pennsylvania Lottery April 24 and won $1.2 million on the number 666, state officials said today.

Gov. Richard Thornburgh said the lottery, beamed nightly to a statewide audience, was fixed by someone injecting liquid into all the Ping-Pong balls used in the game except those numbered "6" and "4." The balls with no liquid weighed less than the others and thus floated more easily to the top of the three air machines used in the drawing.

The winning number 666 paid out a record $5.5 million statewide.

A state grand jury recommended that indictments be brought against six individuals, including a lottery official and the television announcer for the daily lottery drawing in Pittsburgh.

"The grand jury found that a small, close-knit group of persons purchased extraordinarily large quantities of lottery tickets for the April 24 drawing," Thornburgh said.

Acting Attorney General Harvey Bartle said about $500,000 in tickets have yet to be cashed, and will not be honored if they are.

Despite lottery officials' assurances that they had control of the game "every minute," the grand jury found lax security. On the night of the rigged drawing, the three lottery drawing machines were left unattended for 30 minutes, the jury said. And last-minute drawing preparations were left to Nick Perry, the television announcer for the drawing at WTAE-TV.

The investigation of the lottery began after Anthony Grosso, described by the state crime commission as the "acknowledged numbers baron in Pittsburgh," told reporters that the April 24 drawing had been fixed.

State revenue secretary Howard Cohen, whose agency runs the lottery, initially discounted the possibility of a fix. His resignation was announced today by Thornburgh, although Cohen reportedly is not under investigation in connection with the April drawing.

Named by the grand jury were Perry, Edward Plevel, a Pittsburgh district manager for the state lottery; Peter K., Jack K., and James Maragos, and James Maragos' wife, Jean Maragos. Three other Maragos family relatives were mentioned by the grand jury, but not recommended for prosecution.

State officials said tickets were purchased in bulk at Pittsburgh, Phildelphia and in south-central Pennsylvania.

The tickets were bought on all combinations of four and six. They were purchased by members of the Maragos family or by surrogate buyers, including the three other family members named.

In Philadelphia, three members of the Maragos family and another man -- said to be their driver for the day -- bought more than $10,000 tickets at 12 locations -- 2,000 in one delicatessan alone.

The grand jury said that the family spent more than $20,000 for 50-cent tickets. A total of $1,037,000 was bet on April 24. The state lost almost $2.5 million that day.

The tickets, as well as records of telephone toll calls, played a major part of the investigation, which was conducted primarily by the Pennsylvania State Police. One toll-call record, according to an official close to the probe, showed a call from Peter Maragos in Philadelphia to Nick Perry at the television station in Pittsburgh on the day of the drawing.

A state justice department spokesman said the case is a "matter of continuing and intense investigation." He refused to say whether there is evidence of any possible riggings before April 24 or whether the alleged scheme was tested before April 24.

Today's lottery news caused consternation in other state capitals where lottery income has become an increasing source of revenue for hard-pressed state governments.

It is one of the five largest state lotteries in the country.

Locally, Maryland runs a popular state lottery that uses a Ping-Pong ball system almost identical to Pennsylvania's.

Voters in the District of Columbia rejected a proposed lottery in a referendum last year. Virginia does not have a lottery.

Maryland officials said it would be impossible to rig their lottery using the method the grand jury reported finding in Pennsylvania. Each ball is checked after the drawing. This was not done in Pennsylvania.