"Season's greetings to all our dear friends," began the two-page holiday message from Muriel and Joseph Nellis, a Washington lawyer who is now chief counsel of the House Select Committee on Narcotics Abuse and Control.

The typewritten letter, filled with news of Nellis family activities, is typical of those many families mail out to friends over the holidays, but the Nellis letter differed in significant ways.

It was written on stationery reproducing the congressional committee's letterhead and at least one copy was mailed without sayinf postage through use of the congressional franking privilege. It is illegal to use the frank for any personal communications unrelated to congressional business.

A copy of the Nellis letter received by a Washington Post editor came in a House committee envelope marked "official business" and bearing the congressional frank of select committee's chairman, Rep.Lester L. Wolff (D.N.Y.).

Asked about this, Nellis said some of his personal holiday greetings were mailed from the select committee's office on reproduced committee stationery. But Nellis insisted stamps, rather than the congressional frank were used to mail them.

The committee counsel maintained that only "10 or "12 of his friends got such official greetings, while the rest of his friends were sent more typical season's greetings mailed from home.

The Nellis' Christmas letter began, "Muriel and I are taking this round-robin means of addressing our greetings and sending our love and good wishes for a happy, healthy and prosperous New Year. In the year ahead we will be doing quite a bit of traveling and look forward to the prospect of seeing all or most of you again.

"For those of you who are not aware of Joe's present activity, the letterhead tells the story. He has taken a leave of absence from his law office to become chief counsel to the House committee named above."

Nellis said yesterday he used the congressional stationery - which lists the name of Wolff and 17 other congressmen who are members of the select committee - "to let people know where I was."

Rep. Wolff said yesterday he previously was unaware of Nellis' season's greetings. "He tells me that he sent out several letters and put on stamps," the New York congressman said. "I certainly would not condone" use of the congressional franking privilege for such messages, he added.

The first half of the letter was devoted to describing how Nellis was asked to take the job as committee chief counsel and how he met President-elect Carter. "Quite a number of Joe and Muriel's friends will be working at top levels in the new administration," the letter added, "and that of course always makes Washington a better, more fun place to live in. THe doldrums of Nixon-Ford have already begun to disappear. . ."

It is not uncommon for members of Congress to use their official stationery as a format for Christmas greetings mailed by paid postage, but a congressional aide said in recent years there have been no reports of holiday greetings having been sent out by congressional frank.

He said that one Capitol Hill secretary, however, was required to refund 13 cents to the federal government after she used her congressman's stationery and franking privilege to write a personal letter of complaint to a department store.