Boston — Casino gambling has entered New England quietly through a back door. While civic forces and many public officials have teamed successfully to keep gaming interests from coming into the region with Atlantic City-type operations, dice are rolling and roulette wheels spinning around Massachusetts. And it all may be perfectly legal, or soon will be, much to the concern of antigambling activists, law enforcement officers, and some legislators.
The problem, as they view it, is the alleged infiltration of some so-called ''Las Vegas nights,'' sponsored by nonprofit groups for fund-raising purposes, by criminal elements.
Particularly concerned are district attorneys John J. Conte of Worcester County and William D. Delahunt of Norfolk County who are pressing hard for tougher regulation of such gaming activities.
Mr. Delahunt has warned that unless corrective legislation is passed quickly, he is ready to challenge in court the legality of ''Las Vegas nights'' under an existing statute that permits fraternal and charitable organizations to hold raffles and bazaars.
If these gaming enterprises were ruled outside the exceptions permitted by the law, all such operations across the state would be prohibited immediately.
Voicing strong allegations of underworld involvement in ''Las Vegas night'' operations, district attorney Conte told members of a legislative committee that ''if there are any doubts about this, I'll show you the names, I'll tell you who the underworld characters are.''
That casino-type gambling has become rampant in the Bay State in recent years is at least partially underscored by the number of such activities, which increased from 517 in 1979 to 1,261 last year.
While prospects for passage of legislation to outlaw ''Las Vegas nights'' appear slim, support is growing for tighter controls to make sure that the proceeds from such operations go to the sponsoring organizations and are not siphoned off by racketeers and professional gambling promoters.
Pending legislation would make the Massachusetts Lottery Commission responsible for overseeing and regulating these fund-raisers.
One measure, moving quietly along until Delahunt and Conte, among others, raised their concerns, would allow those sponsoring such gaming operations to keep more of the proceeds and give the state less.
If this were approved, income to the commonwealth would be reduced to between
The smaller take would not pay the expenses of the Lottery Commission's overview of the operations, according to agency officials.
Charging that many Massachusetts charities are ''getting ripped off by shady promoters,'' state Rep. Lawrence R. Alexander is pushing a 13-point substitute measure, including a limit of three ''Las Vegas nights'' a year per charity. He notes that at one location there have been at least 65 of these money-makers since last February.
His proposal would empower municipal officials, on a local option basis, to prohibit such activities and require promoters to obtain a permit for each function rather than an annual license.
He would set maximum nightly cash prizes at $2 to $5 rather than $25. The much lower limit on prizes, he contends, would discourage ''professional gamblers from taking advantage of amateurs running Las Vegas nights.''
Meanwhile, big-time casino promoters are still trying to get a foothold in New England.
Nevada-based MGM Grand Hotels Inc., having been thwarted at least temporarily in their efforts to bring their gaming operations to Massachusetts, now are looking longingly to the north in New Hampshire.
Although the initial proposal, now being readied, includes only a rebuilding of the fire-destroyed Rockingham Park horse race track and construction of a convention center, the long-range plan includes a casino.
Although hardly enthusiastic over the prospects of having casino gambling in their midst, New Hampshire officials are increasingly anxious to get the raceway , whose revenue is sorely missed, back in operation. Despite the continuing opposition of Gov. Hugh J. Gallen to an Atlantic City or Las Vegas-type setup in New Hampshire, the MGM Grand proposal, with the possibility of a casino later on , appears to have a chance of being approved.
The opening of such operations is a major concern to antigambling forces throughout the state and in neighboring Massachusetts.
Interest in the Rockingham tract by the Nevada firm comes at a time when most Massachusetts lawmakers appear cool, if not outright opposed, to a proposal to clear the way for casino gambling. Last spring MGM Grand purchased a 58-acre tract in the coastal town of Hull, south of Boston, for a proposed $100 million convention-gaming center.