It is tremendously difficult (and many times even dangerous) to In any way knock Jean Shepherd, the humorist-broadcaster-writer who has amassed more totally loyal fans than Kirk Cameron, or even Tony Danza. Shepherd, who used to conduct the all-time great radio talk show around these parts on WOR-AM, has gone on to make a super name for himself in the big screen movies ("A Christmas Story') and all over TV. "American Playhouse" already has given us two of his random reminiscences of Middle America life in the good old days - "The Great American Fourth of July and Other Disasters" and "The Star-Crossed Romance of Josephine Cosnowski." They were both warm and wondrous, funny and human and believable, Shepherd at his humorous best. The same praise, we must hasten to add, applies to "Ollie Hopnoodle's Haven of Bliss," Jean's latest "American Playhouse" flick, which comes along tonight at 9 via Channel 13. Why then the big buildup about the perils of knocking the sassy Mr. Shepherd in the first place? ***** OK, so here goes. Along with being a quite talented water, Jean is the possessor of an extraordinary ego. (Don't take our word for it, take a look some time at a piece he did for the New Jersey Network, in which he cruised up and down the Turnpike in a huge stretch limo, slurping champagne and making Robin Leach-like comments about the good life.) He has a hard time keeping himself out of the pictures he creates. And this time, he has written a nifty 90-minute comedy and then stretched it to two hours, just so he could squeeze in a funny part for himself. Unfortunately, the additional half hour, which comes at the very beginning of "Ollie Hopnoodle," has not very much to do with the rest of the piece and only serves to clutter it up, to keep us from the film's meat and mirth. (Aw, Jean, Jean, you gotta restrain yourself and stay out of the wonderful way once in a while. As an actor, you're a marvelous writer.) ***** All that being said, let us now sing the praises of most of Shepherd's latest serendipity-doo. Just in time for the summer vacation season, Jean has a marvelous go at recalling that great American ritual of '50s yore, when the family packs up and heads for the annual two weeks at "The Lake." With James Sikking (as far away as possible from his "Hill Street Blues" role) as "The Old Man' and Dorothy Lyman as the ubiquitous Mom, we follow the hilarious and incredibly perilous journey of the Parker family to Ollie's place on the lake, complete with five cabins named after the Dionne Quints. Our protagonist is 14-year-old, Ralph played to a teenage tickle-thee-well by Jerry O'Connell of fond "Stand By Me" memory). Now grown up (and with Shepherd serving as off-camera narrator, a role much better suited to his talents), Ralph still can't get over the terrific times the family had just getting to their vacation idyll. So we follow the Parkers in a cantankerous old red Chevy, loaded inside and out from top to tied-down trunk, with every possession not nailed in place at home, all of which Morn insists "may come in handy, you never can tell." The object, of course, is to get an early start, like 4 a.m., "to beat the traffic. "Ah, but you know that just isn't going to happen. It's mid-morning when the family gets going along the highway of their vacation dreams, with the younger son, Randy (Jason Clarke Adams), whining every mile of the way. (All together now, what would a kid like that say over and over again? Right! "Are we there yet?") ***** Randy, who gives new meaning to "car sickness" is not the only obstacle in making this a completely happy, sappy journey. The car overheats, there's a flat tire, a stray bee decides to join the family fun, Ralph remembers he forgot to pack the fishing gear, Morn just has to stop at every roadside stand and, wouldn't you know it, DETOUR! All this is captured by Shepherd in his unique, understated, hilarious manner. There are many individual scenes in the film that are funny, but there are two that are fall down, spin around laugh-out-loudable. In one episode, they are stuck (seemingly forever) behind a truck loaded with molting chickens. In the other, the detour leads them 'round and 'round in an unbroken circle of delight. Throughout it all, despite disaster and doubt, the family manages to remain cheery and anticipatory about what Iies ahead. And tagging along with them this way should make our own vacation plans just a little bit happier to put together. OK, so the only thing that bothered us was the Shepherd ego shtick In the opening 30 minutes. It had very little to do with the remainder of this lovely piece of humor (although Shepherd as the terribly tyrannical owner of Scott's Used Furniture Mart might well be the subject for some future project). It just keeps us from getting on with tonight's treat. Oh. Yes, and one more bit of self-indulgence. There's a delightful dog called Fuzzhead who has a featured role in the first 30 minutes and, wouldn't you know it, the cute little canine is actually Shepherd's own family pet, Daphne, who obviously got the job through relatives. Oh well. Don't let all this picky picky keep you from watching "Ollie Hopnoodle's Haven of Bliss." It s super fun. Just don't worry If you come in around 9:30. We promise you haven't missed a thing.