WASHINGTON (AP) _ Red ties bloomed like American beauty roses on the shirt fronts of lawmakers as the United States Senate took an exploratory and cautious first step into the world of television.

On Thursday, for the first time in the 197-year history of the legislative forum that bills itself as ''the world's greatest deliberative body,'' television cameras focused on senators debating on the Senate floor. And for the first time one didn't have to be seated in the galleries overhead to see the debate.

But one did have to be in the Senate or in one of its office buildings.

Until June 1, gavel-to-gavel television coverage of the Senate is to be an in-house affair only, to be seen via closed circuit cable on television sets in Senate offices.

After June 1, televised Senate debates will be made available to commercial television stations and will be available for use on television news shows.

But the Senate is reserving the right to pull the plug if members are unhappy with the production.

So on July 29 the Senate will vote on whether to continue live and continuous television coverage or to expel the cameras from its chamber.

Although their constituents cannot yet tune them in, senators dressed Thursday as though they could.

Many wore television-blue dress shirts. And many wore red ties - bright red ties, photogenic red ties - that lit the television screen with sparks of color.

Sen. Phil Gramm, R-Texas, wore his red tie as he discussed the federal budget in the afternoon with Budget Committee Chairman Pete Domenici, R-N.M., also in red tie, as were Sens. Lawton Chiles, D-Fla., and Steven Symms, R- Idaho.

A little later, Sen. Warren Rudman, R-N.H., Gramm's partner in crafting the Gramm-Rudman deficit reduction act, appeared on the Senate floor, in red tie, of course.

Senate Republican Leader Bob Dole of Kansas, in red tie, led off Senate Television Day One, noting that senators would spend the day debating the budget and wondering if the results should not be ''X rated.''

Continuing in that vein, Dole said: ''I know one thing, it will be a full- length feature picture. Let's hope it has a happy ending. I don't know about the rest of my colleagues, but I'm not looking forward to a tear jerker.''

Dole said the Senate's experiment with television appeared on its first day to be heading toward success.

''Our experts tell me that the technical bugs are being worked out and that our picture is a good one,'' the majority leader said. ''I'm not sure about the debates, but at least we look good.''

And on June 1, he said, ''we'll be available on home TV and ready - and sometimes even willing - for network television news coverage.''

The House brought television into its chambers permanently in 1979.

And many viewers of television's first day in the Senate said they thought because of its free-flowing, more flexible format, the Senate is likely to prove better television than the House.

In the House, members speak from fixed positions, making a stacatto series of brief remarks.

In the smaller, more intimate Senate, television cameras, remotely operated from a control room in the basement, can focus on each of the 100 desks and pan the chamber, providing atmosphere in the process.

Senators can speak from their desks and, if they wish, roam the floor.

''If there were ratings, the Senate would sweep them,'' said an enthusiastic first-day viewer of Senate television.

But as might be expected, that sentiment encountered disagreement in the House which does not share the Senate's traditions of unlimited debate.

Just wait ''until you listen to those people talk for 35 or 40 minutes,'' advised House Speaker Thomas P. O'Neill Jr., D-Mass. ''You wouldn't believe there could be so much wind and so few people.''