Tom Stoppard's television play "Professional Foul," at 9 o'clock tonight on Channel 26, comes in on little cat's feet, and with a sermon in its heart besides, but the play still manages to generate considerable and admirable narrative and ideological suspense. It's an ingeniously urgent piece of work.

"Foul" is not an example of Stoppard the wordsmith as in his "Real Inspector Houn" and other stage pranks: the subject is an ethical crisis in the life of a man who has managed through most of his life to avoid ethical crises by objectifying them into issues.

He is forced into confrontation with the practical while attending a seminar on philosophy in Prague, where he is approached by a political dissident who has a thesis to be smuggled out of the country. The professor at first refuses - "It would be bad manners, wouldn't it?" - but his moral isolationism is pierced when he learns the youth has been summarily arrested and when he himself is detained by secret police.

The menace of a totalitarian society is conveyed with cunning economy in Stoppard's script and through the meticulous direction of Michael Lindsay-Hogg; Peter Barkworth is eminently convicing as the professor. For television the play is too word-heavy, even though the professor voices the observation that "language is as capable of obscuring the truth as revealing it," and some of the characters depicted as boors are allowed to prove the point all too well.

But there is an essential, civil sincerity to the play, and some of that may be due the fact that Stoppard himself was searched and detained while attempting to leave the Soviet Union in 1977 with a petition, signed by Russian intellectuals, he intended to deliver to Amnesty International the London-based group that calls world attention to political prisoners and won the 1977 Nobel Peace Prize. Stoppard was relieved of his petition by the gray men of Russian customs.

"Professional Foul," a BBC and WNET-TV coproduction, is the first of three "Great Performances" pegged to the theme of "Human Rights." One wonders if this theme would have been adopted if the phrase were not a catch-word of the Carter administration and the Carter administration were not considered friendly to public television. Oh well - worse things could happen. 'Ringo'

One way minor league luminaries try to enhance their status is by running around trashing the concept of success. The more thay protest the rigors of being idols, the more they reinforce the myth that they are idols indeed.

"Ringo," former Beatle Ringo Starr's first solo television special - at 9 o'clock tonight on Channel 4 - is infected with this neurosis. In a twist on "The Prince and the Pauper," Starr plays both himself and "Ognir Rrats," a human blemish who is allowed for a few brief moments the legal high of being the one and only Ringo Starr, passed off here as if he had a following so huge and adoring that the planet can hardly contain it. In fact, Starr's solo albums have been duds and he is a lifeless mumbling cipher on the screen.

This NBC one-hour special, nevertheless, has a lot of catchy cuteness and includes splashy, playful fantasies and dream sequences that should appeal to children. Art Carney, George Harrison (making a brief Rutles homage), Mike Douglas, Vincent Price and the oppressively ubiquitous John Ritter are among the guest stars, and the vehicle remains for the most part harmless.

Watching it is a little like flipping through the covers at a record store; you may not find anything you want to take home, but you don't mind sampling the merchandise.