Republican presidential candidate Ronald Reagan describes his long-advocated plan for cutting taxes 30 percent over three years as simply a "target" that would be applied flexibly depending on economic and budgetary conditions.

But Reagan, in an interview with The Washington Post, expressed "great confidence we can meet the targets."

The inteview took place Wednesday in Shreveport, La. On Friday, President Carter, noting the latest increase in consumer prices, warned that Reagan's tax plan was inflationary and "would be like pouring gasoline on a fire."

Reagan says his tax plan is not inflationary because it would stimulate industry, increase output and generate more federal tax revenues than it would cost. In the interview, Reagan said he hoped he could balance the budget before the 1983 target called for in his economic plan and said if this were to happen, he would propose other "tax reform" or even greater tax reductions than the 30 percent cuts.

In the wide-ranging interview, Reagan also:

Declared he would remain active in behalf of causes he believes in if he does not win the presidency but would not seek office again.

Declined to say how often he would hold press conferences if elected, but said they would be on a more regular basis than Carter's. Carter has held 59 press conferences, averaging one about every three weeks.

Said he did not believe his age has been an issue, hidden or otherwise, in the election campaign.

Acknowledged that he had been "surprised" at the additional press scrutiny given a candidate once he becomes the presidentail nominee.

"It was something of a discovery," said Reagan. ". . .I was surprised at the subtle difference at being the nominee. You're doing the same thing that you did when you were campaigning for the nomination. But suddenly the press is camped at your door every day, every minute. There isn't anything you can do without their attention. As you know, one of the television networks has even rented a tree from a neighbor so they can hang a telephone on it right opposite our driveway. I was surprised by that."

Reagan, who usually has friendly if reserved relations with reporters, was uncharacteristically critical of the press after he made a series of gaffes in the opening weeks of his campaign. While he adjusted to the added scrutiny, there are many who think that Reagan's slow start prevented him from taking full advantage of Carter's political weaknesses.

The 69-year-old nominee said that his campaigh pace in the primaries and his own reaction to comments about his age had prevented it from becoming an issue. "Rather than trying to duck it, we made a joke about it." Reagan said.

Answering a series of questions about what he would do as president, Reagan expressed confidence that he could win support from the bureaucracy for his programs.

The GOP nominee sometimes has been criticized for thinking of Washington as " a big Sacramento," and the examples he gave of what he would do in the White House drew heavily on his eight years as governor of California.

For example, asked how he could expect the bureaucracy's support, if he carries out his pledge to launch his preidency with a hiring freeze as he did in California, he replied:

". . .By attrition, you're not taking someone's job. We never had any layoffs or things of that kind in state government, and when there came a real case of need of some unique employe . . . who had to be replaced, we quietly replaced him.

"But we also found this, and this is what I would count on. I know it's very easy when I talk about bureaucrats and bureaucracies to think that everyone in government is sterotyped as some kind of an enemy. We found with our task forces that the government is full of a lot of people who honestly want to do what's right. . . . Once state employes found out -- and I'm sure this would be true in the federal government -- that there was a legitimate effort being made to eliminate waste and the faults of bureaucracy, they literally came out of the woodwork to help. . . . The task forces told us that the thing they heard most from these employes was, 'Well, we just never thought before that anyone cared.'"

Reagan also expressed the belief that he could work with and gain the cooperation of a Democratic Congress. "I had eight years' training getting along with an opposition in the legislature, and I think there's something new going on in the Congress that people haven't paid much attention to," Reagan said. "I think there's a new element on both sides of the aisle, Democrat and Republican, who aren't bound by party leadership, who are there honestly, with a belief and philosophy and wanting to get things done, and I think they can be worked with."

Reagan held frequent press conferences during much of his two terms as governor, but, as president, "I dont't know how often they could be held," he said, "I have heard former presidents talk about the length of time that it took for briefing on a press conference because the questions can be far ranging and obviously the president can't have at his fingertips all the time everything that's going one, every piece of legislation, and I've heard some of them say there is a limit as to how much time you can give up to prepare for them."

But Reagan said that press conferences should be held "very definitely with some regularity, and I think if should be certainly far oftener than one in five months" as Carter has sometimes done.

Reagan's answer about willingness to be flexible on his tax plan came in response to an observation that former president Ford, while agreeing with Reagan on the need for a 10 percent tax cut in 1981, has said he would want to know what revenue estimates are before committing to a 10 percent tax cut in the second and third year of the plan.

"Many of the economists who have worked on this program believe we're going to find the results are more optimistic than we have stated," Reagan said. "For example, suppose you didn't wait until 1983 to balance the budget -- suppose it happened earlier. If you began accumulating surpluses, you could then change your mind and begin implementing other tax reforms that should take place.

On foreign policy issues, Reagan said his advocacy last Sunday of a SALT III treaty was a logical extension of his frequent campaign statement that the United States should, after rejecting SALT II, sit down with the Russians and negotiate, "as long as it takes," to get real nuclear arms reductions.

In the interview, Reagan also acknowledged that Carter had partially succeeded in making Reagan's positions on war-and-peace issues the principal issue of the campaign. Carter, he said, tried to "create the image of me as being a hard-nosed warmonger of some kind in an effort to avoid having to campaign on his record." An account of that portion of the interview appeared in Thursday editions of The Washington Post.