Seven decades of official atheism made the Soviet Union's communist government the grinch who stole Christmas, leaving behind the secular celebration of New Year's Eve as the main mid-winter holiday.

But like in the little town of the Dr. Seuss children's book, in Russia the Jan. 7 Orthodox Christmas refused to die, and under glasnost there has been a resurgence of interest in religious holidays.In the effort to break traditionally spiritual Russians from religion, when the communists took over they simply moved many of the non-religious traditions of Christmas to New Year, which remains the major holiday of the season.

Families and close friends gather for a New Year's Eve feast and champagne at midnight Dec. 31. Gifts are exchanged around a Yule tree decorated with ornaments. Greeting cards are sent to friends and relatives.

Santa Claus - in Russian Det Moroz, or Grandfather Frost - and his helper Snow Girl may be hired from a state agency for a surprise visit to the youngsters.

Russian Orthodox Christians celebrate the holiday of Jesus Christ's birth not on Dec. 25 as in the West but on Jan. 7 because of the difference between the old Russian calendar and the Gregorian calendar.

Under glasnost Russians are flocking back to Orthodox services, particularly on holidays, in record numbers as churches are allowed to reopen and the official stigma of being a "believer" eases.

Earlier this year, the Soviet Parliament passed a law on religion abandoning the official state support for atheism, but there are still some obstacles to a flourishing of religious tradition.

For example, while Jan. 1 is an official state holiday, Orthodox Christmas Day on Jan. 7 remains a normal work and school day, except in some of the more radical breakaway republics such as Latvia.

Soviet and U.S. State Department estimates for 1989 say about 18 percent of the Soviet Union's population, or about 51 million people, are members of the Russian Orthodox Church. About 2 percent, or 6 million, are members of other Christian faiths.

The Orthodox church says it is unable to give a good estimate of the number of believers in the Soviet Union, partly because for so long many were reluctant to acknowledge church membership.

But as of September this year there were 11,940 Orthodox churches throughout the country. Even with believers allowed to reclaim more and more churches from the secular uses they were given under communism, on holidays there is generally not enough room for everyone who wants to attend services.

And although Easter rather than Christmas is considered the major holiday of the Orthodox church, on the night of Jan. 6 churches around the country will be jammed with people for the three-hour midnight service, the overflow crowd standing outside in the snow.

On Christmas Eve, families gather for a Christmas feast, the traditional "Holy Supper" that ends a 40-day period of fasting for Orthodox believers.

The feast varies from region to region and depends, of course, on the availability of products. Common would be cabbage soup, mushroom soup, stewed fruit, fish dishes and vegetable and fruit salads.