EAST RUTHERFORD, N. J., Dec. 19— All week, Martina Navratilova said that she wanted to prove ''beyond a reasonable doubt'' that she deserved to be No.1 for the year in women's tennis. Tonight, she did, beating Chris Evert Lloyd, 4-6, 6-1, 6-2, in the final of the $300,000 Toyota championships.
''She's No.1, I concede,'' Mrs. Lloyd told the crowd of 9,248 at Byrne Meadowlands Arena after the match. Then, as if to whet spectator appetites for the future, Mrs. Lloyd, added, ''but not next year.''
Miss Navratilova has won Grand Slam singles titles at Paris, Wimbledon and Australia in recent years. But none may surpass tonight's triumph for thoughtfulness and patience. And by using all of the vast resources in her repertory - including drop shots and topspin backhand passing shots -the 26-year-old left-hander showcased the athletic versatility and stylish virtuosity in her game.
''She played more intelligently today than anytime I've seen her play,'' said Dr. Renee Richards, her coach, who has settled Miss Navratilova's ground strokes and worked to give her a clearer tactical picture of important matches.
Miss Navratilova finished the season with 90 victories in 93 singles matches - beaten only by Sylvia Hanika, Pam Shriver and Mrs. Lloyd - and 15 tournament titles in 18 events. The $75,000 first prize raised her earnings for the year to $1,461,055, a single-season record on the women's tour....
.... One difference between Miss Navratilova's approach to tonight's match and the other finals, she said, was in her attitude and diet. Last year, when she lost a three-set final here to Tracy Austin that cost her the No.1 ranking to Mrs. Lloyd, Miss Navratilova said her food for the day had consisted of only Rice Krispies.
''Today, I ate like a tiger,'' she said, reciting oat meal, a waffle, croissants, a whole dish of pasta and bread, ''a couple of melons,'' and iced tea and juices.
In contrast to Mrs. Lloyd, who said she felt pressure-free and played ''relaxed and loose,'' Miss Navratilova described the prematch pressure as ''unbelievable.''
In the end, Miss Navratilova prevailed because she won the key points, a quality long associated with Mrs. Lloyd's reign as a seventime No.1.
Mrs. Lloyd won the first set with a service break in the third game and a barrage of backhand crosscourt winners off Miss Navratilova's attacking serve-and-volley game.
If Miss Navratilova had persisted stroking at one speed, Mrs. Lloyd might have evened their season series at 2-all and compounded the No. 1 question.
Patiently Seeking Chances
But in the first two games of the second set, Miss Navratilova began changing speeds, opening the court and patiently waiting for chances. She saved a break point from 30-40 in the opening game and then broke Mrs. Lloyd from deuce for the first time with a backhand drop volley winner and Mrs. Lloyd's errant overhead and netted sliced forehand.
''I let up just a touch,'' Mrs. Lloyd said, describing the lost break point in the opening game - a long backhand return - as huge. ''But you can't do that against Martina.''
....Miss Navratilova tried six drop shots in the third set and won every point, one off a second serve, another angled and on the run. The drop shots not only lured Mrs. Lloyd in from her customary spot on the baseline and disrupted her rhythm but also set up countless other opportunities for passing shots and attacking volleys by Miss Navratilova. said. ''Everytime she came in, I was comfortable hitting my passing shots.''
Mrs. Lloyd, who collected $40,000 as the runner up, had surprised Miss Navratilova in the Australian Open final by rushing the net effectively. But tonight, concentrating her attack solely on Miss Navratilova's backhand often kept her from finishing some points and gave her opponent the chance to lob or play her way back into the point.
From a spectator point of view, the match was highly entertaining, as both players made spectacular gets, while lunging and stretching and grunting for other shots.
On the sideline, Nancy Lieberman, the former pro basketball player and Miss Navratilova's close friend, shouted encouragement and words of advice.
''Martina used the court better than I did,'' said Mrs. Lloyd, who finished with a 75-6 record for the year, beaten only twice-both times by Miss Navratilove - in her last 44 matches. ''She was patient, took her time, waited for the opening and came in.''
.... ''I told her I thought she was playing great and she had reached the point where she was dominant over Chris and should assert that dominance,'' Dr. Richards said.
Miss Navratilova said she was disappointed that she felt she had to prove her No. 1 status one more time. ''But I'm glad,'' she added, ''because now there's no question about it.''