Following her commander in chief's orders, Nancy Reagan today went to sea, where 5,000 officers and men of this combat-ready aircraft carrier awaited her with the Navy's version of a red carpet.

"I hate to drop names," she told them, proceeding to do that to everybody's delight, "but last night when I kissed your commander in chief goodbye, he asked that I pass along a message. He said, 'Nancy, will you tell them how proud I am of them? How often I think about them, and tell them there are no Americans I have greater respect or affection for than those fellas out there defending us.' I feel the same way."

In an impromptu shipboard press conference, she also voiced support for her husband's doctors, who have been publicly second-guessed by others in the medical profession for delaying a definitive examination of the president's colon until last week.

"You have to understand I'm a doctor's daughter," she said. "My father never believed he should talk about another doctor's case."

She seemed to disagree with the idea that the president will return soon to the Oval Office.

"I think he should be treated as any other patient. He should go through a recuperation period. When I visited some of the children (at Bethesda Naval Hospital) they were being given time to recuperate and he should be allowed to do that."

It was her first daylong outing since her husband was hospitalized, and only once, when she was relaying the president's message, did her voice choke up. She quickly recovered and went on to deliver hugs and kisses to a half dozen surprised crew members celebrating birthdays.

Mrs. Reagan flew from Washington by Marine helicopter with Navy Secretary John Lehman Jr. and her stepbrother, Dr. Richard Davis, arriving here 25 miles off Ocean City, Md., amid gray skies and 25-knot winds. Only a few hours earlier many of the America's crew had read for the first time in the ship newspaper that Reagan's tumor was cancerous.

"We knew he was in the hospital but we didn't know it was cancer until today," said Petty Officer 1st Class Jim Ward of College Park. "Things are slow out here."

The first lady told the crew the president was "feeling better." She described him later to reporters as in an "upbeat mood . . . he cannot wait to get home." When they go to California on vacation next month, she said, she expects it will be "very hard to keep him in the house."

Capt. Richard C. (Sweetpea) Allen, the America's commanding officer, said he had been "quickly reassured" by the White House during the weekend that Mrs. Reagan intended to keep her date to tour the carrier and hear about the Navy's program to combat drug and alcohol abuse.

There were no gun salutes -- "Mrs. President doesn't rate honors," said Capt. Peter Doerr, the ship's chief of staff -- but hundreds of sailors crowded the flight deck, among them 10 white-uniformed "sideboys" there to escort Lehman.

Mrs. Reagan's excitement started to build shortly before her helicopter landed. "She said 'this may be the best therapy for me,' " James Rosebush, her chief of staff, later told reporters.

It was an idea she later repeated to Commodore Jack Ready, commander of Carrier Group 8, which includes the America. Ready conducted a briefing that included warnings about "head knockers, knee knockers and finger jambs" around the ship.

Wearing red trousers, a white blouse, blue-and-white knit vest and blue patent leather, rubber-soled shoes, Mrs. Reagan was a patriotic, if seldom seen, figure making her way among the ship's all-male crew. Because the America is a combat ship, women are not assigned to its crew.

She carried her own luncheon tray and sat down to eat her carrot salad, cole slaw, beef tenderloin and two chocolate chip cookies with several sailors who had won lunch with her as a reward for top performance.

Later, on the hangar deck, wearing a flight jacket with her name on it and a USS America cap, she received for the president a giant get-well card signed by nearly 4,900 of the ship's 5,000 men. It read: "From America's best to America's best. Get well, Mr. President."

"If that doesn't make him well, nothing will," Mrs. Reagan said.

In the forecastle, she heard Capt. Leo Cangianelli, a Navy expert on drug and alcohol abuse, describe Navy procedures in detection and control.

Stepped up efforts including compulsory urinalysis and treatment, he said, had reduced marijuana use among junior enlisted personnel from 47 percent in 1980 to 10 percent last year.

The Navy's war on drugs, he said, could be summed up in the words of a former chief of naval operations: "Not on my watch . . . not in my ship . . . not in my Navy."

"I'm so impressed by what you've done in the Navy," Mrs. Reagan said later. "I can't congratulate you enough."

Up on the flight deck, Lehman pointed out an F14 fighter plane. "It's a bargain at $30 million," he said.

Later Mrs. Reagan watched Navy pilots flying F14s and A6 bomber jets take off and land on the 1,027-foot flight deck. She also saw a Phalanx weapons system fire rounds of ammunition and various maneuvers by the frigate USS Pharris.

The first lady said she found the jet exercises "exciting," but joked that she would suffer heart failure if she had to do that kind of job.