Wives, children, parents, sisters, brothers, grandparents . . . more than 300 relatives of the onetime hostages started converging on Washington yesterday to await their personal reunions with the family members, the reunions that will have been delayed by as much as 449 days.

This morning, after a brief meeting with President and Mrs. Reagan at the White House, about 140 of these relatives will board a jet at Andrews Air Force Base to fly to Stewart Airport in Newburgh, N.Y., and their first chance to embrace the men and women finally returning to American soil.

For the first time since their relatives were taken captive by Iranian militants on Nov. 4, 1979, the families' schedules are suddenly predictable enough to be reduced to written itineraries that have lent an aura of certainty to events after 14 1/2 months when nothing was ever certain.

The nearness of the long-awaited reunion triggered frantic last-moment action yesterday as relatives packed their bags, arranged for neighbors to care for pets, made plane reservations, bought small gifts or tokens of home to be given to the returning family member and tried valiantly to despose of the endless number of other small details that needed to be dealt with.

"We're going in circles," said a breathless Bonnie Graves as she excused herself to a caller, saying that she was overwhelmed with preparing for her husband John's return to Reston. "We have travel plans to make, all kinds of preparations . . . . There are just so many interruptions."

"The excitement?" asked Lisa Moeller, wife of Marine Staff Sgt. Michael Moeller, as she tried to sort out all the things left to do in her Quantico home. "It'll catch up to me later. aI really don't have time to get excited now. Probably it's the same for most of the wives. They're trying to get the house cleaned up, get packed, calm down the kids and make sure there's enough cat food and cat litter . . . ."

Sometimes, neighbors and friends were able to help a little. One neighbor of Barabara Timm, mother of Marine Sgt. Kevin J. Hermening, brought by the house a package of pork chops after hearing a television report that Kevin had requested a dinner of barbecued pork chops when he reached home.

"It's just a mess," said Pat Lee yesterday as she tried to do a load of laundry, pack, board the family dog at a nearby kennel, ready her Falls Church home for the arrival of her in-laws this weekend, wash her hair, and make sure her 11-year-old daughter, Dana, was ready to go.

"I've had 14 1/2 months. I should have been ready," she said, laughing.

But despite the help of neighbors who have made sure her refrigerator was full and the dishes were washed over the past few days, the constant interruptions of phone calls from old friends and acquaintances from the Midwest to Hong Kong to Germany have given her little time to think.

When she and Dana travel to Newburgh and West Point for the meeting with her husband, Gary, it will be somewhat of an accomplishment if she remembers to bring him the new sweater he requested, plus two of his pipes and a pouch of his favorite tobacco.

Vivian Hohmeyer, coming to Washington from Vinton, Iowa, for the reunion with her sister, Kathryn Koob, is bringing along some popcorn and "a heck of a bunch of sausage."

Carol Elledge, sister of Army Sgt. Joseph Hall, is bringing a brand-new red, white and blue outfit from her Kennewick, Wash., home. "I might as well be patriotic if I'm going to do this thing. I'm going to look like a flag."

Michael Moeller had asked his wife not to bring along anything special for him, but Lisa Moeller said she had brought a new movie camera to record his reunion with daughters Celeste, 5, and Lindsey, 3, and would be bringing him some new clothes.

Few of the relatives had the time yesterday to talk or even think about the former hostages' reaction to their new freedom and to the worldwide attention suddenly focused on them. Lisa Moeller, however, was able to pause long enough to worry about one future problem.

"There's the fact that people are going to treat them like monkeys in a zoo. They're going to say, "They're all cranked up. Let's be gentle,'" she said. "Why don't they just treat them like they're them. I understand the stuff about the media, but there comes a point when, no matter how badly you need the story, the hostages should be left alone. Not because they can't handle it, but just that they shouldn't have to handle it."

But there appears to be little likelihood of a letup anytime soon.

On Thursday, for instance, communities across the country will be participating in a nationwide religious service of thanksgiving for the hostages' safe return.

The idea started with Susan Wagner, a special assistant comptroller of the currency in Washington. After watching some film clips from the hostages' last Christmas in Tehran, she decided to urge everyone "to show them how much we all care" by holding the services.

Her call was picked up by Protestant, Eastern Orthodox, Roman Catholic, Jewish and Moslem religious organizations, which sent mailgrams to 247,000 congregations around the country.

There will be special services and ceremonies in the communities the ex-hostages call home, too.

In Seaford, Del., for instance, home for Marine Sgt. Gregory A. Persinger, a parade complete with colored banners is scheduled. The 600 tickets for the homecoming dinner are already sold out. And Mayor William A. Slatcher has proclaimed the next seven days "Persinger Week."

Mrs. Moeller said that two little girls in the neighborhood told her they wanted to plan a party for her husband.

"Michael's more likely to go for that than some big hoopdeedo," she told a friend on the telephone. "You know, like a friend of mine says, when it's a child you know it comes from the heart. It's the adults you have to worry about."