Barnard Hughes theorizes that the same actors keep coming back in slightly different form every generation ot two.

Tom Hanks is Jimmy Stewart, Hughes said, while he is a hybrid mixture of crusty character actors Gene Lockhart and Walter Connolly.Hughes pulled a copy of a letter from his pocket that had been circulated to agents' offices by a producers trying to cast Grandpa Vanderhoff in "You Can't Take It With You."

The memo said they were looking for someone "spunky, wise, drool (sic), embraces life, a Barnard Hughes type,"

'I thought the drool was rather nice," said droll, wise, but not particularly crusty Hughes.

"It's wonderful if you fall into one of those types," he said in an interview. "Not only did Gene Lockhart pave the way, but when you walk in people know exactly what to expect of you. You've just got to be crusty to get a few laughs. The battle's won, instead of having to start in and establish everything."

What has the mold for the Barnard Hughes type been doing lately?

His CBS Series, "The Cavanaughs," is on hold, but Hughes is hopeful. He particularly enjoyed working with Art Carney on that one-the two old pros amused themselves on the set exchanging the names of long-gone vaudeville teams.

He also stars with Sada Thompson and Robert J. Prosky in Home Fires Burning (Sunday at 8 p.m., Ch. 5).

There he is again-spunky, crusty, droll and wise-as Jake Tibbets, editor of a small-town Southern newspaper during World War II. Thompson is his long-suffering wife and Prosky his equally long-suffering lifelong friend.

There is an edge of bitterness to Tibbets, and it involves his son, Henry, now a combat soldier in Europe, from whom he is estranged.

When Henry is first reported killed in action, then is found to have survived and returns home, family relationships stretch to the breaking point.

The show offers a warm, affectionate and compassionate look at America when everything was smaller and slower, when communities did not have the great homogenizer of television to make one place so much like another.

"It was fun to do," Hughes said. "I was working with dear old friends."

Among them was producer-director Glenn Jordan, with whom Hughes did some Chekhov one-acters in New York a few years ago.

Jordan endeared himself to Hughes and the other New York actors in the cast by having The New York Times Sunday edition mailed to him in the little Georgia town where "Home Fires" was filmed, then making copies of the crossword puzzle made for everyone.

"The script was literate, intelligent and pretty full of stuff for us to do," Huhghes added.

He also is putting in some work for nthe federal government this year-TV movie-wise, that is.

Hugh played Secretary of War Henry L. Stimson in the upcoming CBS movie about the start of World Was II-"day One," to air March 5.

He also starts work this month playing CIA director William Casey in the CBS movie "Guts and Glory: the Oliver North Story," which may air later this spring.

"Guts and Glory", Hughes said in disbelief. "There must be some mistake. I can't be in something titled 'Guts and Glory.'"

He already is hard at work learning more about Casey.

"I've been reading Bob Woodward's book on Casey, 'Veil,' and there was a wonderful article in The New Yorker magazine about the Reagan administration that has a lot of good stuff in there about Casey that was useful.

"Bob Woodward described him very well but I want to hear his voice. I don't want to do an impersonation of him, but I do want to find out a few things. I know he walked with his arms swinging and he shhok hands like this," Hughes said, demonstrating an aggressive, downsweeping extended hand.

Hughes and Casey had a tendency to mumble, which may have been why he failed to be named to cabinet posts where mumbling was not part of the desired public image.